On the track breaking in the motor...

I am not sure exactly what it was that led me down the path to this particular insanity. Perhaps it was my love of single cylinder race bikes and my love of unique machinery coupled with a near zero budget. Or, perhaps I was crazy to begin with.

For months, while I successfully raced my GB500, I searched want-ads. I pestered people. I measured motors. I measured frames. I asked stupid questions. Finally, I decided that the optimum frame for a Formula Single was a 1991 TZ250. In '91, Yamaha changed the motor to a V-twin and narrowed the frame, but still gave it a long wheelbase. I figured that would leave room for just about any motor. And, confirming my suppositions, Franz Volpe brought exactly that combination to Willow Springs ('91 TZ250 frame/TT600 motor).

I couldn't find a rolling chassis, so I started telling everyone I already hadn't bored to tears about my proposed project. Still, no chassis. It was now mid-season, and since I knew the project would consume more time than I could make available, I was anxious to get started. So, I started going through old issues of Roadracing World looking through the want-ads. Almost immediately, I found a 4-month-old ad with a bunch of RS125s and buried in the middle was a '92 TZ250.

It wasn't the year I wanted, but the price was right, and with all my measuring I was convinced I could make a Honda motor fit. So, I called the number listed and discovered it was Yoshi at the Garage Company in Culver City, CA. Yoshi had imported the bike from Japan, and hadn't been able to sell it. We quickly came to an agreement on a price much lower than that advertised.

So, now I had my TZ. The next weekend was a race weekend, so after a quick check of fluids and fasteners I just had to ride it. That ride convinced me beyond any doubt that I had made the right chassis decision. Handling was better than anything I could have even imagined.

I think my GB became jealous of the new stable-mate and grenaded its motor in practice. That motor went away for repair. In retrospect, not keeping the motor under my control was a big mistake.

In October, I made the big commitment and stripped the TZ down to bare frame. I bought a clapped out XL600 as a motor donor. Over the course of the next few months, the fun got really intense.

The '92 TZ frame is really tiny. I had to make the engine mounts three times before I got it exactly right. If the engine is tilted too far forwards, there is no room for the exhaust. Too far rearwards, the carb won't fit. The difference between these extremes is minuscule. With the engine mounted, there is about 1/4 inch clearance to the sides, and just enough room to mount a very contorted exhaust. The sprocket lines up perfectly.

Once I had the engine mounts figured out, it was time to fix the motor. When I bought it, there was the worst rod knock I had ever heard. After a few phone calls in which I got conflicting information about XL vs XR rods, I ordered a new XR rod from IMS in Riverside, CA. The crank and new rod went off to Luttig Performance in Montclair, CA. I also gave him my cylinder to bore to 102.4mm so I could use a new piston from Thumper Racing, Marshall TX.

I got the pieces back a week later and started putting the motor back together. A problem I still faced was carburation. The XL motor I had was a two-carb model, and there was no way to fit two carbs inside the TZ frame. I planned to use the GB500 head and its Megacycle cam. Getting it back from the mechanic I had originally given it to turned into a nightmare. Finally, after I threatened him, he gave me the GB motor back. I could then finish assembling the new motor.

With the motor back together, I could concentrate on minor details like the remote oil tank, oil lines, and gas tank. I cut and bent an oil tank to fit between the seat frame rails and delivered it to a welder.

Two weeks later, he told me that he didn't think he could do the tank after all. Meanwhile, I had dropped off the stock oil lines at a hydraulic hose shop with specific instructions how to modify them. Three weeks later, they finally "finished." They had taken beautiful steel lines, chopped them down to about 1 inch long and soldered on fittings. They used push on fittings and water heater hose to make lines the length I requested.

I was pretty upset at these developments--definitely seeing the gas tank as half empty rather than half full. And, as it turned out, this wasn't even the low point of the project.

I changed welders, and refused to pay for the butchered oil lines. The new welder took my oil tank parts and gas tank with instructions and cardboard mockups. The local hydraulic parts supply (Deering Industries, Long Beach) was happy to provide a ton of Aeroquip parts, for a price. Meanwhile, I picked up a used 41mm flatslide carb, so a call to Sudco for setup advice and a trip to Scotts Performance in Montrose was on the agenda. I also swung by Flanders in Pasadena for a custom fitted throttle cable.

In just a few days, I got the new oil tank back from welding. It looked great. But, a few days later while discussing the gas tank modifications, my welder suggested pressure testing the oil tank. I was a bit surprised, but thought that maybe he was just busy and forgot to do it himself. So, when I got a chance, I checked the tank. It leaked like a sieve. I'm glad he remembered it needed to be checked before I mounted it over my rear tire, filled it with oil, and killed myself when it leaked oil on the tire.

I was now down to the wire. Only a few days left before race weekend.

The oil tank went back for more welding. I took half a day off on Wednesday to visit my welder and impress on him how anxious I was to have the bike ready before Friday came and went. He assured me that I would have everything in plenty of time. His watch must run differently than mine since I didn't feel that the interval between Wednesday afternoon and Thursday night was "plenty of time."

Thursday evening I stopped by again, at least he had the oil tank done. And he had cut the bottom off the gas tank. He told me that he would get the tank done that night and drop it off at my house Friday morning on his way to work. I am a bit wary of those type of arrangements--having been disappointed by them in the past, so I told him to call me immediately whenever it was done so I could drive over and pick it up.

At midnight, with no word from him, I nearly conceded defeat.

He must have finally realized how serious I was. I got the call at 1:00 am Friday morning. So, at 1:30 I had my gas tank. But it had no valve, and he had decided that welding in the original petcock mounting plate was too hard. Instead, I had a 1/8" npt flange on the bottom of my tank and no valve.

At sunup, I was driving like a madman to every car parts store I could find looking for a valve. Finally, I gave up and went to the hardware store and bought a refrigerator ice maker shutoff valve. With a little creative soldering, I had a working solution.

I filled the gas tank, and with a feeling of deja-vu, watched gas drain out of weld holes almost as fast as I poured it in the top. I dug out some old 5 minute epoxy and patched as best I could. When it held most of the gas I poured in, I pushed the bike out to the street for a test run.

The motor had not been run since I built it (no gas tank, no oil tank), so I pushed it around awhile to get the oil circulating. Then, with a new sparkplug and the untested wiring hooked up, I clicked it down (race pattern) into 2nd. A quick run, then jump on the seat while letting out the clutch to turn the motor...nothing. The rear slick just skidded down the street. OK, I just clicked the transmission into 4th and tried again. Still nothing, although this time the motor went past top center. Again. Nothing. Once more. Still no hint of a spark. Once more. Now I'm at the end of the block half a mile from home, and nothing.

I'm panting like a dog, and this pig still won't even fart. I do the run-jump-dump the clutch over and over on the way back to the garage and never does this ugly piece of crap even hint that I've done anything right.

When I get home, it's 9:30 in the morning. It takes 2.5 hours to get to Willow Springs. I decide that I can either push it 'til I die, or go to the track and borrow some rollers. At least then, I would know for sure if it might start.

So, I loaded it up and left. When I arrived at the track, it was noon. With a sense of impending doom, I unloaded the trailer and pushed the bike over to Danny Farnsworth's rollers. This was it. The culmination of three long months of 16 hour weekends fitting, cursing, struggling, and accidently cutting myself on the band saw. I had no reason to believe it would even run, but I had to give it a shot.

Choke on, 4th gear, clutch in, grab the front brake--rollers starting, tire spinning, ease out the clutch...I can hear the piston chuffing as the motor turns over. After an eternity, the thunder rolled. It was the bark of an angry junkyard dog. What a glorious noise!

The jetting was all wrong, so I scrambled to find parts that would at least approximately work. That quickly done, I ran (actually walked quickly) to registration and happily payed my money.

Out on the track, I nearly had an emotional moment. This project had been my undivided obsession for three long months, and it was finally running on its own power. What a feeling.

I spent the weekend chasing jetting, never getting it quite right. And there are several things that need fixing; for instance the exhaust grounds hard in fast right-hand turns, and properly fixing the gas tank. I came in last among the finishers of my Formula Singles race, but like in the Special Olympics I felt I was a winner because I made it to the competition.

The Naked Bike

I left the track in good spirits with a long list of improvements the "Mongrel 620" needed.

To start with, I am aerodynamically challenged--no, let's amend that to "gravitationally endowed".... Even if the jetting was perfect, my little motor just didn't have the power to pull me around. And, it certainly didn't have the power I expected based on the work I had done to the motor.

When I got the bike home, I set to work. Well, not really. I had to wait a week because my darned job gets in the way. It's unfortunate that my boss actually expects me to do stuff for him. The unsympathetic barbarian....

With the motor apart on the bench, I could investigate the mysterious lack of power. I suspected the new piston, so I started with that. Calipers, dial indicators, burette full of light oil, and a big mess later, I had an answer. The "high compression" piston I had bought and installed in the enlarged bore actually yielded far lower compression than stock. And, stock, the XL can just about run on anything wet.

After a desperate search through my piles of catalogs and notes, I found suitable replacement. I ordered it, then had to endure another long week waiting for UPS to deliver it.

I finally received my new piston. It was beautiful. It was gorgeous. It was shiny. It was loads heavier than the one I had. Bummer. I installed it anyway. The previous piston had a big hump in the middle. This one, a perfectly flat crown (except for the valve pockets). I clayed the head. 40 thousandth's clearance for the squish band, 80 thou for the valve pockets. Perfect.

That was two weekends gone, two to go. Next, I decided I'd better get busy with paint since I've decided I don't like owning a yellow motorcycle--especially one with welding burn marks all over the top of the gas tank.

I had a great scheme. I could get leftover bits of Imron from my aircraft mechanic friend. I had a great plan. I'd strip the tank, sand the bodywork, and we'd shoot the paint in a couple of weekends. Lots of red. Some gray, some white. It would look great.

My wife told me, "I didn't bother you while you were building the bike, but now I have a list." "You have to spend more time with the family." She, who must be obeyed, decreed that we spend a whole weekend out in the RV together. In Arizona. Didn't she realize I had a timetable to keep?

Three weekends gone. One more left. Not enough time. I was spending 12 hours every day at work, 1.5 commuting, 20 minutes for eating the dinner my wife worked hours preparing for me, 15 minutes quality time with the kids every day, a little time to sleep every night.... Maybe I could get things done in time after all.

The Imron pain plan went up in smoke. At the last possible minute, I grabbed a can of black Rust-oleum and covered everything I could. Naturally, it ran and sagged everywhere. I always want to put the whole can on and be done with it. Over the next couple of days, I sanded and re-painted twice. Finally, I got about the right amount of paint on so the runs weren't too bad. It only had to meet the 50-50 rule (look good fifty feet away at fifty mph), anyway. Fortunately, I had covered the front number area--at least it was still yellow and I could use it for a number plate. No time to paint it white.

The motor was back in the frame, and most of the fairing was painted. Now, I had half a day to work on the exhaust. No problem. I clamped it in the vise and cold bent it slightly. I got it mounted in plenty of time with thermal wrap to keep the waste heat away from the engine. I was ready to go. It was Thursday night.

Out on the track on Friday morning, I kept the engine running slow to seat the new rings. Boy, that sure was fun. By lunch time, I couldn't take it any more. I just had to open it up. In the first after-lunch session, I rolled open the throttle. It not only made more power with the new piston, but the jetting wasn't nearly so bad as before, either.

I thought to myself, "Wow, this is actually working pretty good. I didn't do a half bad job. There's enough power I could probably get this thing going fast enough to race."

Jetting still wasn't perfect. There was a bit of a rich hesitation at half throttle, and it seemed somewhat lean on top. So, just to smooth the throttle transition, I changed the idle jet down a size, and went up two main jets.

Back out on the track in the last session of the day, I whacked open the throttle to test the new jetting. I nearly dropped my teeth. The Mongrel ripped at my arms as it blasted off like a rocket. In that moment, it transformed from "pretty good" to "man, that's exactly what I dreamt of when I started this project."

The next morning, I had a chance to test the power against a Ducati SuperMono. Larry passed me through Willow's high speed turn nine (I freely admit I'm both slow and afraid of that turn...) As he accelerated down the 1/2 mile front straight, I decided to see what my Mongrel was made of. Full throttle. Upshift at redline. Unbelievable, I was actually gaining on him across the start/finish line.

He disappeared around turn one, and was gone. I couldn't follow at his pace. It wasn't the bike. It was me. I just don't yet have the skills to ride that fast.

Basically, the Formula Singles race on Sunday was a six lap repeat of that. This bike just laughs at me for going so slow in the turns. I came in last again. But, I know I had the most fun last weekend.

I still need to do something permanent about the exhaust, and the transmission gearing is terrible for racing. I need to make an airbox. The paint needs re-doing. So, the project continues....

On the bench...

Development priority number one seemed to be the transmission. With the XL gearing, engine speed dropped 1700 rpm between gears. That seemed to me to be just a bit too much. Someplace, I had heard, or read, that one of the differences between the XR motor and the XL was a closer ratio gearbox in the XR. So, off to the local Honda shop I went.

I figured I'd just order whatever gears I needed and drop them in for a quick improvement. This month, I'd have my mechanical work done early so I could spend some time with my family for a change.

At the shop, I nearly fainted when the parts man told me the gears were about $100 apiece. Let's see. Main shaft and countershaft, five sets of gears...$1,000. I don't think so. And, while talking with him I discovered that the microfiche listed exactly the same transmission gear pairs for both the XL and XR. Puzzled, I bought a set of fiches for the XL and XR.

Back at home, I studied the fiches and verified the bad news. The only difference between the XL and XR was primary gearing. Since I had the reader fired up, I looked at the GB500 parts fiche. Imagine my delight when I found the GB had exactly what I was looking for.

Not only did the GB have a tighter gearbox, I just happened to have most of a GB motor in the garage (see my GB racer story for details). So, I split the cases on both engines.

The transmissions are not identical. But, with both apart, I could make direct comparisons between the two. As luck would have it, M2, C3 and M5 were interchangeable. And, those were the gears I needed to change to set the ratios right. So, I did. In theory, the engine would now only drop 1300 rpm between gears.

As I reassembled the race motor, a thread insert I had previously installed pulled out of the cylinder. Rats. I had used up my weekend working out the gearing, so it was a long week at work before I could deal with the ripped thread insert.

The next weekend, I headed to Scott's Performance in Montrose. Several weeks before, they had offered me an XL cylinder for a good price, and I figured that now was a pretty good time to take them up on their offer. At Scott's, I looked at the cylinder they had. It looked near new. And, more importantly, the head bolt threads looked new and sharp.

With both cylinders in hand, I headed all the way across Los Angeles County to see George at Luttig Performance in Montclair. He bored out the "new" cylinder, and kept the old one to build a solid insert to repair the bad one.

Back home, I put the cylinder on the bottom end, and quickly found out why the threads looked so good. They had been retapped from 8mm to 9mm. Imagine my aggravation....

With new inserts in all the holes, I finished assembling the motor. For good measure, I clayed the head. Everything was fine. 1mm in the squish, 2mm valve to piston. But, when I put the head back on after measuring the clearances, another thread insert pulled loose. Those darned Honda cylinders are made of a processed cheese-like product. Grrrr.

Back to Montclair. George had inserted a piece of tool steel in the first bad hole. It looked pretty good. So, we traded cylinders and I headed back home.

Everything went back together smoothly, this time. Once the engine was back in the bike, I had time to think about where this project was headed. I'm still the slowest guy out there, but nobody has more fun. So, I decided that I needed to enter the California State Championship Series. That would give me a meaningful reason to try Sears Point and meet all the other crazy Singles guys in Northern California.

So, I sent in my money. I packed my stuff in the RV, and got ready for an easy session at Willow Springs. I expected to get a good test of the new gearing, work on speed in the tighter part of the track, and just have a generally fun weekend. Then, in two weeks, I could change the counter sprocket for a bit lower gearing and go play at Sears Point.

I had arranged to share paddock space with Silverman Museum Racing during the NASB/FUSA Willow Springs race weekend, so I headed out Thursday afternoon. Thursday evening was great fun. Also sharing paddock space was Gary Rothwell, the hooligan motorcyclist from Liverpool. He is the guy who does the incredible wheelie/stoppie/burnout/etc. shows. Really nice guy. We had a great evening drinking beer and telling lies.

Friday morning, I set out for an easy practice session. And blew up the motor getting on the track.

I was accelerating between turns one and two. As I shifted, I heard the horrible sound of over-revving, then that gut wrenching noise of lots of money being dumped into a blender. I coasted off the track, and that was it for me. No easy weekend of practice. No State Championship series. No fun.

I have stripped the motor and learned that I'm very lucky. The heads broke off both exhaust valves, and beat a hole in the piston. One valve head fell through the hole and jammed into the counter-balancer drive gears. This forced the balancer 35 degrees out of sync from the crank. The balancer and crank then smashed together, immobile. I apparently pulled in the clutch in the exact fraction of a second that everything locked. I was that close to being spat off.

So, it's back to the (very expensive) drawing board....

The disclaimer

My wife was none too thrilled when I told her how much the carnage would cost to repair. After I convinced her that it was in her benefit to keep me happily busy working on the race bike, I made the decision that, since this is in all probability the last time she will let me rebuild a race motor this year, the Mongrel would be reborn with no compromises.

In a take no prisoners state of mind, I paid a visit to Brian Uchida at HRC, Honda's racing division. Brian was polite as he asked what I had and what I was doing with it. He seemed genuinely interested. But, Brian would be a tough opponent at Poker. He gives nothing away. Occasionally, as I described what I had done to the motor he would smile a tiny smile, and nod his head imperceptibly.

Once I had shown that I actually had some idea how the RFVC motor worked, he gave me the choice of a 75mm or 80mm crank. He advised against the 80, but I just had to have it. With my 102.4mm bore, the Mongrel would have a monster 660cc displacement, up from the previous 620.

I could see that Brian was not happy with my decision, but he disappeared into the racks of trick racing parts. A moment later, he reappeared carrying a beautiful mahogany box.

After he had carefully set it on his desk, out of my reach, he turned and asked with a smile, "Tell me about the piston you are going to use." I could see the trap he was setting, and quickly gave him the correct answer. Again, the barely visible smile and nod. "Well done, grasshopper, you have now truly proven yourself worthy...."

Unfortunately, Honda no longer provides HRC with RS600 heads. I did get a dimensioned drawing of the HRC recommended exhaust system for use with this motor. And, it bears very little resemblance to anything currently available for the RFVC motor.

I picked up a new stock XR600 head from Mid-Cities Honda (562)531-1225 for a very reasonable price. I took the head to Luttig Performance and gave it to George. He had agreed to test it on a flowbench and do whatever minor clean-up the intake and mexhaust needed.

While he was looking at it, I saw that gleam of excitement gearheads get when they suddenly get a challenging project. He handed me the head and said, "Look in the intake port. Now, rotate it down about 3 degrees." I looked in, and saw that with some welding and totally reshaping the intake, the flow would be straight to most of the intake valve head. So, he now has the head to weld and re-shape the ports. So much for the simple "clean-up" of the ports.

During the same visit, we chucked the flywheel in the lathe and cut off about 3 pounds of excess rotating mass. It's not light by any stretch, but it's three pounds lighter than it was.

George is also re-valving and re-springing forks and shock so they can better cope with my excess mass. We discussed what should be done, and were in agreement. He apparently wanted another opinion, so he asked his good friend Eddie Lawson (!) what his opinion was. Eddie agreed with our assessment. George told me later that once Eddie stopped laughing at my Mongrel, he said he'd like to try it. Hmmmm, maybe I could get some valuable feedback....

We are currently having some trouble finding springs that are heavy enough and still fit inside the TZ250 forks. But, that should be resolved this week.
We'll probably haul the old springs down to Showa and go through their books to find the right ones.

Flowbench testing of the stock head showed us that the radical cam I've been using is far more lift than the head can efficiently use. I know that HRC has a cam with a bit milder lift, but a bit more overlap, than what I have.
There may be another visit to HRC in my future.

Once I get the head back, the motor assembled and back in the frame, and the suspension installed, I'll have the HRC exhaust made and fitted. It sounds simple, but there's only two weeks left before the next race, and lots of details to work out between now and then. But, I've had enough of being patient. I am going racing in June!

Exhaust specs

Note: click here for a full size version.

Friday, June thirteenth. Friday the 13th. I'm not superstitious, but I was beginning to notice the omens. I was on my way to practice, and it was raining. My wife had scheduled a conflicting social engagement for Saturday. I tripped over our black cat in the dark. I should have paid attention.

On the way to the track, I had two hours to reflect on the previous two weeks. George had welded the inlet ports nearly closed, then re-cut the intake port roof a little higher. Half an inch higher. He also reshaped the exhaust ports. The results were astounding.

Anyone who is honest about porting an engine will admit that it is usually very difficult to make any meaningful improvement to a modern factory port.
In fact, it is very easy to find reduced flow following a porting job. I have seen a head done by one of the more famous tuners that flowed significantly less than stock. This head had improved flow at all valve openings.

Because of the flow figures, and the trickness factor, I called Brian Uchida at HRC and ordered a new cam. During our conversation, I told Brian that I considered the lift too high on the cam I had been using. After I had explained my reasoning, he told me, "Yes. Other people racing this motor have told me those cams lift too high. These motors aren't happy with that much lift." I wish I knew half of what he knows (and doesn't tell until you figure it out for yourself)....

The bad news (and there is always bad news somewhere) was the suspension.
Neither George, nor I could find appropriately heavy springs for the TZ250 forks. We had agreed that if we couldn't succeed with a last ditch effort involving cutting some FZR springs, the forks and shock would go back together with stock springs--but different valving. So, that's what he did.

The worst news was the steering damper. It had been leaking badly and had more air than oil in it. George agreed to refill it, but when he had it open, he thought he might as well take it apart and clean it. That turned out to be a mistake. Among the really intricate valves in this particular damper was a Teflon coated copper seal. The seal needed a special tool to recompress it before it would go back into the damper body. George didn't have the tool. Ooops.

I had a spare damper from my Ducati race bike, so I calmly gathered all my pieces and went home to build a racing motorcycle. The suspension went in easily, and the motor went together with no problems. Well, I did have one small setback. The clutch plates had banged little divots in the clutch basket fingers. I didn't like the looks of that, so I pulled the basket, the center, and the matching primary gear from my poor GB500 and bolted it all together. Oh, and the HRC cam dictated changing the rocker assembly because it wasn't compatible with the one I had been using.

Anyway, I stuffed the engine back into the frame, and slapped on a smaller rear sprocket because of the primary gear change. That was all easy enough, but the steering damper was a problem. The spare just didn't have quite enough travel. I set it to give me as much travel on both sides of center that I could, and crossed my fingers for luck.

The next step was to haul the assembled bike to C.D. Engineering (714)632-9150 so that Clyde could build a new exhaust from the HRC dimensions and fit it to the bike. I showed him where I wanted it mounted, how it had to clear the front tire, and gave him the dimensioned drawing.
With nothing else to do--I went home.

Two days later, Clyde called and frantically asked, "The exhaust is done, but I haven't had a chance to fit a silencer. Can you wait to pick it up until this afternoon?" I was stunned. I hadn't planned to pick the bike up for another three days, and even so, I was concerned that he wouldn't have time to finish the exhaust. I needn't have worried.

The bike was ready in plenty of time for that Friday practice. On the way to the track, the weather cleared. It was perfect, slightly cool and sunny, with no breeze. I was stoked. I tried hard to be patient. I tried to push start the beast. It laughed at my puny efforts. I borrowed a set of rollers and it fired right up. It sounded great through the new pipe. I couldn't help but laugh as I rode it slowly around the paddock to heat cycle the engine.

It took great force of will to let it sit and cool before I re-started and rode out to the track. The off-idle power was incredible. I'd just crack the throttle and it shot ahead. Wonderful. I accelerated up the hot pit lane, and entered the track.

Half throttle laps are pretty boring, but everything felt great. After two or three laps, I increased the pace a bit. It felt willing and balanced. So, I started using more throttle. Then a bit more. Finally after about ten laps, I was on the front straight. I did a quick run up to redline, then shifted up. A loud BVVVVVVV from the engine told me I had a problem.
Switch off, clutch in, I coasted to a stop. I had no idea what the sound was, but previous strange noises had meant very expensive repairs. It wasn't the same sound, but still....

After I pushed it back to the pit, and changed out of my leathers, I looked at the engine. Oil was slowly dripping down from between the head and cylinder. Blown head gasket. I could live with that. But, my fun was over for that day.

On the way home, I tried to think of anything I could berate myself for. Nothing came to mind. I had used extra care building the motor because of all the parts changes. I just couldn't think of any reason for losing the head gasket. That bothered me. Mechanical failures always have an underlying cause, and I didn't like the uncertainty.

When I pulled the motor apart that evening, I discovered two of the head bolts had pulled out of the cylinder. This was the cylinder that I had already put Timeserts into all the holes. Now, the inserts were pulling out of the cheesy aluminum cylinder. Heat and too many rebuilds had taken their toll.

Saturday morning, cylinder in hand, I headed to Luttig Performance. My spirits sank when I pulled into the parking lot and saw the closed sign.
No need to panic, yet, though. Clyde at C.D. Engineering had told me that he had so many projects he would be working all weekend. So, I drove down to see Clyde.

"Hey, Clyde. I need an emergency repair!" Without hesitation, Clyde dropped the project he was working on and took the cylinder. He is a really terrific guy.

Since the holes had already had conventional inserts which failed, Clyde started cutting a couple of whopping big inserts on his lathe. Midway through the job, his lathe became recalcitrant. It would only run on one phase of current. After about 45 seconds, it would overheat the relay and trip off-line. We spent some time trying to fix it, but just couldn't find any tangible problem. There's one of those darned omens, again.

Clyde finished the inserts, and I was on my way. I was also nearly out of time--remember that social engagement my wife scheduled? I drove home like a madman, and feverishly began to reassemble the motor. I torque bolts in a two-step method. I bring them all up to about five pounds below the final torque, then bring them all up to specs.

Everything was going great. Until I applied the final 5 foot pounds to the last head bolt. The resistance didn't increase. Another pulled insert. I now had a huge dilemma. I had passed the point of no return. Earlier in the day, I could have dusted off my Ducati and prepped it to race. But I had committed to the Mongrel. So, now I had to decide whether or not I should risk a known bad head bolt.

A saner man than I would have stopped and waited until the job could be completed properly. But, I am a race junkie and it's been three months since my last race.... I had the jones bad. I gritted my teeth and finished putting the bike together.

Sunday morning, I headed for the track. Doubts were gnawing at me. But, my craving was even stronger. I rationalized my mechanical misdeed. The motor had held together with *two* bad head bolts for ten laps. This time, there was only *one* bad bolt. All I needed was eight laps to finish a race. Surely the gods of racing would allow a desperate addict to finish eight measly laps.

I sat out practice. I didn't want to use up any of my engine's limited life with something so trivial as practice. So, I had nothing to do but worry about the motor, and be really annoying to everyone else in the paddock.

By the time my race was called, I was a nervous wreck from hiding my dirty little secret all day. I pushed the Mongrel to the rollers, and didn't even smile when it fired to life. I eased it gently forward into the hot pit. Then I had to sit there with the motor running, using up precious life units, while the crash crew picked up some clown who crashed on his cool-down lap. I was sure the motor would spew its guts at any moment.

Blowing up a motor while engaged in wheel-to-wheel combat is honorable.
Blowing up a motor in practice is just part of racing. Blowing up a motor while waiting for your race in the pit lane is a shameful disgrace.

Finally, the starter let us out onto the track for the sighting lap. The Mongrel leapt forward eagerly. I had to use some restraint since this was still a brand-new motor, and I had no experience with the new suspension.

From the grid, it seemed to take forever before the minute board went sideways and the green flag dropped. I was finally racing. And I had no idea when the motor would quit. Or, if the suspension would spit me off on my asphalt.

I was running with everyone else when I heard a strange whistle underneath me. I backed off the throttle a bit. The whistling went away. I grabbed a bit of throttle. The whistling came back. Great. "I must have a small leak. I'd better take it easy; maybe I can finish anyway," I thought. It took the whole first lap to realize that the whistle was the slide rattling in the carburetor. The new exhaust was enough quieter than the old one that I could now hear it.

I laughed at myself, and picked up the pace. But, I was now far enough behind that all I could do was keep from being lapped. I had the track basically to myself. I had a great time becoming acquainted with the new Mongrel. The handling was night-and-day different even without heavier springs. Power didn't hit as hard as I expected, but there seemed to be plenty of it everywhere.

Overall, the entire bike just felt "right". It had poise that I'd not felt before. I'm now anxious to begin finding the new limits. And, adjusting the one remaining piece which keeps me slow--my mind.

Stock head on the left, modified head on the right.

Other than a quick engine tear-down and rebuild to repair the loose head bolt, there was nothing to do over the past month. So, I took a break from machines (both the motorcycles at home and the computers at work) and took my wife backpacking in the Sierras. A week away from civilization. I found that to be a nice break from the stress of building computer applications at work during the day and trying to run a race development program at night. I was actually happy to be back at work after that vacation. My mind was clear and I felt refreshed.

Because there was so little to do between races, race weekend arrived with no tension or hurry. I packed up and headed to the track early Friday.
When the sun came up, it was already hot. I had to take it easy because I had a newly honed cylinder and wanted to seat the rings. I went out with the beginners.

The Mongrel ran great. I tried to run a bunch of 75% laps to seat the rings. I was defeated by the unpredictability of the beginner riders.
I settled for a bunch of 40% laps. At least the rings had an easy day. Other than a jetting change for the heat, everything was ready to go by the end of the day.

Saturday, I was determined to try running at race speed for the first time. It's been a long time since I ran at those speeds. This year, I've been stymied by the development teething problems.
Last year, I ran the GB which couldn't hope to run that fast. The year before, I raced a Ducati which, until I crashed, was the last time I actually went fast enough to get a knee down on the track. Two years of mental cobwebs to brush away.

In the second session, I began touching my left knee in turn 3. Three is a steep, and sharp uphill turn to the left. In the past, the turn surface was always so rough I wouldn't dream of touching there. So, I was caught a bit off guard. But it sure felt good to carry some speed in that turn for a change. The new suspension was working wonders.

At some point during the afternoon, a few of us were sitting in some sparse shade trying to think cool thoughts. The temp was 105. A small breeze was blowing, but not cooling us much. In a vapid attempt at encouragement, someone suggested that it felt like we were in the Bahamas. A few moments thought and discussion revealed that for what we were spending to race each month, we actually could fly to the Bahamas every month. So much for encouragement. Everyone wilted a bit more after that realization as we asked ourselves, "Why are we doing this?"

During lunch, I decided that my "Blocks 'O Wood" tires had finally rolled their last. They were old when I got the TZ, but I hate throwing away something that isn't completely used up. I hauled my wheels over to the Dunlop truck and paid a small fortune for a set of tires that actually indented when I pushed with my thumb. They sure looked shiny and new.

On the track, those shiny new tires had about as much traction as a well polished bowling balls.
Man, was I terrified as both front and rear slid sideways through turn one. Turn two was no fun either. After that, they kind of held through the turns for two laps--but not much. Once the first two laps were past, and I was reduced to a quivering pile of jelly, they held firm. I felt glued to the track.

The real eye opener was turn nine, one of the fastest turns on the track.
Previously, I felt very nervous in nine. As I crept around it at about 95, everyone else would go screaming past. Now, without the slight walking toward the outside of the turn because of stiff old tires, I knew I could carry more speed. So, I added another five or six mph. And everyone else still went screaming past. At least I can work on that now.

I got one more good session on the new tires on Saturday. I was finally pushing hard at my own mental speed limits.

Sunday dawned hot and still. Even the desert flies were finding shade to rest in. I tech'ed the Mongrel and found a small patch of shade to park it in so the fuel wouldn't boil in its black gas tank. I went out in the first practice. Everything felt good. I felt confident. I felt fast.
Until Stu Knigge blew past me on a Woods Rotax. That man is fast. I suddenly felt all wobbly and slow.

Because of the heat, I started the day feeling physically drained. I compared headaches with a friend. He rhetorically asked, "Everyone here is physically destroyed by this heat, they're mentally a wreck fighting a blinding dehydration headache, and their tires are overheated. You need to trust their skill and judgement at 140mph while you hold it WFO through turn eight, inches apart.
Are we crazy?" The refrain, "Why do we do this?" started beating in tempo with my throbbing headache.

My race was the second of the day. Thankfully, there was little time for nagging doubts to crush me. I was soon on the grid surrounded by eleven other thundering Formula Singles racers.
Just before the start, the thunder lessened slightly as Stu's Rotax stalled. As he pushed it to the side of the starting grid, I thought to myself, "That's it. We're in a war of mechanical attrition and I'm going to triumph through superior engineering." Several laps later, he blasted by me like I was chained to a post. He made it all the way to 3rd place before the finish. He is *really* fast.

I got a bad start. Apparently, everyone else did, too. I slipped the clutch halfway to turn one. I was still in the middle, just where I started. Over the past couple of months, I'd become accustomed to having a clear line through Turn One once everyone left me behind, but this time I nervously threaded my way around the turn hoping I wouldn't smash into anyone.

By turn two, we were all in a fairly close single line. From there, it was mostly straightforward. I kept the leaders in sight for the first two laps, but I lost them, and everyone else, on the third. I hadn't passed anyone, and I didn't know if anyone was behind me (at least until Stu blazed past) so I realized I had to pass at least one person if I didn't want to be last. So, on the third lap, I pushed just a bit harder and passed the guy in front of me going through turn seven.

I set my sights on the next two riders ahead of me, who were battling between themselves for position. Unfortunately, I didn't quite reach them before the checkered flag. As it turned out, there had been someone behind me from the start, so my finish was 10 of 12.

For the first time in two years, I have a bike that can carry serious speed, and now I can hammer it. This sure is fun again. Now, I remember why I do this...I can hardly wait until next month.

Turn Four

What a weekend!

While prepping the Mongrel during the month, I found some stress cracks radiating from the rear tank mount. It was also leaking fuel, again. I left it with Clyde, at CD Engineering (714)632-9150, with the instruction, "I don't care what it takes, or what it costs; make this tank right and make sure it doesn't leak."

The next weekend, I picked it up, and it was stunning. I was stunned too, when I learned how much it was going to cost me--only *half* as much as the first, botched job. I guess there's a lesson in there somewhere. For good measure, he straightened the slightly bent seat rails and made new seat fastening mounts--all included for no extra charge.

I still hadn't worked out how I was going to add speed to the Mongrel. Next to last place is fine once, but I want to do better. But, for that, I needed more speed. "Where do I get more speed," I pondered? Suddenly, it hit me. Red Paint! Ask any Traffic Cop. Red is faster.

Since I had Thursday afternoon free from work, I decided, right then, to repaint the Mongrel. Out came the sandpaper and Krylon. This time, I managed to stay patient enough to not try to empty the whole can in a single coat. No runs, drips, or sags ruined my day this time. Unfortunately, I only had time to paint the fairing upper. It looked much better than before. And, I just knew it had to be faster.

Friday, I purposely practiced with a different group than I normally do. I didn't want any other Formula Singles Pilots to know I had found the answer to more speed. I was blazing, I was blasting, I was rocketing around that race track like nobody's business. And, I actually did go a couple of seconds faster.

In the afternoon, I happened into Kent Kunitsugu, the Editor of "Sport Rider" magazine. I tricked him into taking a couple of laps on the Mongrel. After he came back in and took off his helmet, he stood in thoughtful silence for what felt like a very long time, then delivered his verdict. "With another 10 horsepower, this bike would roost the Over bike [the OV-16]."

OK, so what's the bad news? I know it will shock some of you, but.... He weighs about 120 pounds less than I, so the suspension couldn't have been much worse. I'm so heavy, the front end feels like it's welded to the ground. It didn't work that way for Kent. As the engine tried to rotate the bike around the rear axle without my bulk onboard, the front became too light. He had bad headshake accelerating out of all the fast turns. The jetting was a bit rich, too, and coughed a bit when he backed off the throttle (So, what's the problem? Just keep it WFO....)

I dropped the main jet a couple of sizes, and although Kent didn't ride it again, I think he would have been pleasantly surprised. I think I got back about five of those missing 10 horses right there. At least, the throttle response was alarmingly immediate after that.

He also commented on the power delivery. The Mongrel pulls hard up to 7000 rpm, with a 7500 rpm redline. That's a lot of wasted engine speed. I suspect it has to do with my choice of the 80mm stroke crank. The rod/stroke ratio is probably all wrong. Nevertheless, I made my decision and now I'm stuck with it--at least until I grenade the motor again.

Saturday, I followed the same tactic of not practicing with the other Formula Singles riders. That's a double-edged sword. They don't get to see what you've got, but you never get to test yourself against them until the race. Still, I thought it was more important to try to follow some really fast guys around, hoping to improve my cajones to power ratio.

Sunday, race day begins with two short practices. A riders meeting follows, then it's show time. Mine was the first race of the day. As usual, I was gridded in the back. I got a fair start, leaving a couple of SRX's behind before we all got to the first turn. Once through the turn, everyone was pretty much single file. The race leaders were already pulling way. I never saw them again.

Directly in front of me were two guys who have developed a huge rivalry. As they passed and re-passed each other, they did a great job of blocking the track. With my low cajones to power ratio, I never did quite build the nerve to pass them. At the finish line, the three of us were less than a bike length apart. At least, I improved my finish position from last month. Seventh this time, instead of ninth.

It was a fun race, even if I never saw the leaders after the start. Now all I have to do is: a) corral those missing ponies, and b) improve my own power ratio.

Now, I'm going to take a moment to be deadly serious. A rider died at the track on Friday. I wish him and all those who have met their fate on a motorcycle "Godspeed."

Falling off high speed motorcycles is inherently dangerous. If you race, or ride fast, you *will* fall. You owe it to yourself, and those around you, to buy and use the best protective equipment that you can afford.

The rider, that died, brought his wife to the track because it was her birthday. Some birthday present.

He lost control of his motorcycle cresting Willow Springs turn Six. I was behind him, but watching my line on the track, not him, so although I don't have any answers; the skid marks on the track show a violent tank slapper which ended in a ferocious high-side.

At some point, his helmet came off. He hit the ground with no helmet, and succumbed to his injuries on the way to the hospital. When they recovered his helmet, the buckle was still fastened. Apparently, the helmet did not fit properly.

He might not have survived even had his helmet stayed in place, but he would have had a chance. Without it....

Please, if you're unsure how a helmet should fit, ask. If you're riding with an old helmet (more than five years old), buy a new one. If you're riding fast without leathers, spend a few dollars and get some. If you can't afford new leathers, buy some used ones from a racer who gained weight.

Remember, it does no good to buy the best if it doesn't fit, or if you never wear it while you're riding.

I'm sorry to be so preachy and negative, but I fervently hope that if we can learn a lesson from these tragedies, and another life saved as a result, they will not have happened in vain.

The new, faster red paint.

Life is a really interesting past-time. Just when you think everything is in a nice comfortable rut, chaos breaks loose and events conspire to break the somnolence. These past few months have been especially unruly.

Following the death at the track discussed earlier, my wife and I came to an agreement. I would race fewer times per year, and she would buy me a sailboat. So, now I have two of the most expensive hobbies know to mankind, one of which is a hole in the water into which I throw money. Also, I was promised (then finally given) a new position at work. That was an entire stressful story in itself, but it has nothing to do with Thumpers, so I'll spare the details.

This month, my barely preteen daughter was planning to have a group of her friends over for the night on race weekend. My wife suggested this would be a good month for me to race. I agreed. I had a couple of things to do to the Mongrel first, however.

I was deeply concerned about the lack of power near redline. I was also concerned about the lack of power a thousand rpm shy of a redline. It really bothered me. So, I scratched my head, thought hard, and lacking any clue, fell asleep.

One other problem I could do something about easily was providing cool air to the carburetor. As it was, air blew across the 350-degree F (194 C) cylinder and straight back into the carb inlet. Not exactly an optimal arrangement. My intent had always been to build an airbox. So, one beautiful afternoon I set to work. A quick trip to Aircraft Spruce and Specialty in Fullerton yielded a chunk of blue polystyrene foam, some glass fiber, and epoxy resin.

Back in the garage, I shaped the foam to fit between the frame rails, seat rails, motor, fuel tank, and upper shock mount. Once satisfied with the fit (about five minutes and a "good enough for government work"), I sloshed epoxy resin all over and stuck a few bits of cloth to the foam. Most of the cloth was my shirt and pants, but at least some of it was the glass fiber. After it cured, my plan was to dissolve the foam away with acetone. I had never done that before, but the method came highly recommended. I was looking for a quick fix, so I hadn't wanted to fool with release agents or barrier films. What a dummy I was.

The acetone dissolved the foam with a satisfying crackling sound. I just loved the way it was quickly eaten away. I just hated the blue snot that was left over. Once the foam wasn't foam anymore, all that was left was a gooey blue mess. I scraped out what I could, but no matter what I tried, there was still goo remaining. After an hour of frustration, I decided to just let it harden then sand it out. Another bad idea. Once hardened, the stuff was impervious to anything short of thermonuclear fusion.

So, reaching into my bag of tricks, I did what any professional would do. I grabbed a can of spray paint and painted over the evidence. It doesn't look too bad, if you don't peer too closely.

I still needed to address the power delivery problem. But, race weekend was only one day away, so as a quick fix, I wrapped the exhaust header in thermo wrap. I bought it years ago to shield a custom painted fairing from exhaust heat, but never had any real use for the stuff other than that. Allegedly, the stuff keeps the exhaust gas temperature high for better scavenging. The effect is supposed to be the same as lengthening the exhaust. I thought if I could effectively lengthen my exhaust, it might raise the point of peak power enough in the rev band to mitigate my problem. Besides, I already owned the stuff, so all that would happen was I might have to take it off again--I had nothing to lose.

Race weekend dawned cool and clear. Perfect weather. Yes, I know the rest of the country is blanketed in snow, but I have to put up with lunatics and idiots the rest of the year to enjoy perfect fall weather in southern California.

During my first practice session, I was amazed at how much different the two simple modifications made the bike feel. The motor pulls right past redline. There's still a distinct peak before redline that I want to get rid of, but response is crisp and authoritative. I found I was 500 rpm higher everywhere on the track except my least favorite corner--Turn 9. In Nine, I was a full 1000 rpm faster. That's an astounding change. Unfortunately, I'm already using the smallest rear sprocket made for the TZ250, so now I have to change the primary gearing inside the engine in order to benefit from the increased speed.

I had four or five good practice sessions, then it started to rain. OK, so the weather didn't stay perfect. At least it stopped raining during the night, leaving Sunday clear and bright. I wish I could report that I had the most exciting race of my career, but it just didn't happen that way. I was gridded in my usual third row spot, got a good start, and passed one erratic rider during the first lap. After that, though, I had the track all to myself. I droned around and around until I finally got the checkered flag for 6th place. It's the best finish I've had this year, and the bikes running better than ever, but it was a somewhat anticlimactic finish to an otherwise entertaining season.

Over the next couple of months, I'm going to tear down the Mongrel so I can make the internal gearing change and fiddle with some other things. I've already heard that the class leaders don't plan to return to Formula Singles next year. It could be they're just bored with winning all the time, but maybe, just maybe they have heard the Mongrel nipping at their heels and realize that next year it might not be quite so easy to outdistance the junkyard dog.

New carb set-up

I was sitting in the garage dejectedly wracking my brain for a solution to the Mongrel's inability to deliver power above 6000 rpm. I had the piston, I had the cam, the head was flowed, I had the secret HRC exhaust. What could I do? Scratch calculations told me I needed a bigger carb, but I couldn't find a 54mm carb anywhere. My musings were distracted by the Mikuni calender on the wall. Something about the lady on the calender suddenly caught my attention. The answer was right there in front of me . . . a pair of 38's.

A pair of 38mm carbs has a cross sectional area of 2269mm compared to a single 54's 2289mm. I just happened to have a pair of Mikuni 38mm flatslides left over from the TZ250 motor I had sold. I measured. They just barely fit side-by-side between the frame rails. Eureka!

I loaded the Mongrel onto the trailer and hauled it and the carbs down to Clyde Dennon at CD Engineering. He looked at me like I had a hole in my forehead, "You want how much carburetor on that thing? It'll never work." I let him know I wasn't looking for expert opinion. I just wanted him to build me a manifold to fit the carbs between the seat rails, moving the rails if necessary.

My plan was to modify the flow-bench developed head I already had. Remember, I'm cheap. I really didn't want to buy another head. This plan was shattered when I retrieved the Mongrel from Clyde. The manifold was beautiful. But there was a 3/4 inch mismatch between the outside walls of the inlet tracts.

I was a bit miffed, but Clyde explained his reasoning for building it as he did. To fit the carbs in the small area available, the choices were a really tight radius turn into the existing inlet, or massively widen the inlet opening in the head. I had to agree with him. Unfortunately, that meant buying a new head and heavily modifying it. The head modification fell, once again, to George Luttig at Luttig Performance.

George's initial reaction was disbelief, "You want to mount how much carburetor on that motor?" I assured him that I had not completely lost my senses and explained my thinking. He was still skeptical. So he thought a moment, then reached for his Rolodex. "Eddie will know." Eddie Lawson wasn't home. "Wayne is in the area; he might know." Wayne Rainey wasn't available either. George started flipping through the Rolodex and stopped at a card with the name "Parker."

After a short conversation, during which George's eyebrows shot up, he scribbled some hasty notes. "You're right. Forty-eight to 54 mm is right for that motor."

We discussed what I wanted done to the head. George thought he'd like to give it a try. So I left the heads with George and went home feeling satisfied I was on the right track. Full of confidence, I went on vacation.

When I returned, I could hardly sit still waiting to get back to George's to see what miracles he had wrought with the head. Beauty is in the eye of the beholder. I beheld a masterpiece. George had welded the stock inlet nearly closed, and added material to other places so he could create two separate inlet tracts which matched the manifold Clyde had built.

While I was away having a fun vacation, George had been slaving over a flow bench and his die-grinders. The results were nothing short of amazing. We had been concerned about losing flow compared to the last, single inlet, head George had done for me.

It's very difficult to improve flow in a modern head. It's next to impossible to radically alter an inlet (e.g., chop it in half and move the halves apart) and improve the flow still further. George had managed the impossible. The head now flowed better than ever before.

In ecstasy, I went home and immediately swapped heads on the Mongrel. The next day, I called Paul at Sudco to order tuning parts for my TZ250 carbs.

"What do you mean parts aren't available for that carburetor?" I hung up in disbelief. Positive there must be some mistake, I called Mikuni. I was politely told that the '92 TZ250 carb was a proprietary design specified by Yamaha and used only that one year. No tuning parts were interchangeable and none were available in appropriate ranges for four strokes.

Not quite ready to surrender, I thought, "What the heck, it's only money" and ordered a pair of brand-new 38mm Mikunis.

When they arrived, I rushed out to the garage to install them. They didn't fit. The new carbs were half an inch wider than the TZ carbs. That meant the centerlines of the inlets and centerlines of the carbs absolutely couldn't match.

Dejected is not a strong enough word. I was stunned by my stupidity. So much effort. So much time. So much money. All wasted by my arrogant assumption that I could make a 2-Stroke carb work on a four-stroke motor. I was ready to push the whole thing over a cliff. I just shut the garage door and walked away.

A few days later, in the middle of the night, I sat bolt upright in bed. I knew the answer. At least, I was pretty sure I did. I couldn't wait any longer to test my theory.

When my wife discovered me in the garage an hour later, I was standing at the workbench in boxer shorts with calipers in my hand, jets in the other, and surrounded by dismembered carbs, muttering to myself. She must've seen the maniacal, feverish gleam in my eyes so she quietly backed out of the garage and returned to bed without saying a word.

The next morning, I impatiently waited in the parking lot for George to open Luttig Performance. When he arrived, I excitedly showed him what I'd discovered. "If you cut the shroud off, like this...then turn down this part, cut some threads here, put a slot here...it's a direct replacement."

George calmly picked up some calipers and measured a few places, studied the nozzles and carbs a few moments and said, "Yes. You're right. That would work. But, I'm not going to do it."

He must've seen my eye start to twitch and my hand slowly move towards the fork leg on his workbench. He quickly reassured me, "I have a better idea." My eye stopped twitching and my hand returned, empty, to my side. He went on to point out that if he modified things my way, I'd be forever stuck with needing custom parts for every little tuning change at the track.

Instead, he proposed to modify the carb bodies themselves. I was instantly intrigued. We examined the carbs, compared them with my new carbs, and decided it just might be doable. I left the carbs in George's capable hands.

A week later, I returned and was rewarded with two newly modified carbs.
Before he handed them to me, George looked at them, then at me. He chuckled, and said, "You know, I shouldn't give these to you. In ten years, someone else will be holding one of these carbs in his hand while he talks to Mikuni on the phone. 'I don't care what your book says, I know what I have in front of me.' Nobody will ever believe him."

George had done a masterful job machining the internals of the carb within less than half a thousandth so that I could now use standard tuning parts.

Finally, all the pieces had come together. The manifold to hold the carbs, the head to take advantage of the twin carbs, new throttle cables, and finally the twin carbs themselves. I was ready to test myself on the unforgiving battlefield of the racetrack.

Saturday, I was at the track before the sun rose. The air was just perceptibly warm and still. In the desert, this is a sure sign the day will be scorching hot. This is the most (actually *only*) beautiful time of day in the desert.

As the red ball of fire climbed above the eastern horizon, I had time to reflect on my new jetting dilemma. I had no real idea where I should start with jets, pilots, air screws, needles, slide cutouts, etc. With less intake vacuum the carbs should need leaner jetting. And the blazing heat of the day would require leaner jets. And the low air density (something two smoke tuners worry about all the time) calls for even leaner jets. But, leaner than what? I certainly didn't want to guess wrong and melt the piston.

I had not been able to get any reliable recommendations for these carbs, everyone still said, "You can't use TZ carbs on a four stroke." So, I took my best guess and hoped for the best.

With the aid of borrowed rollers, the Mongrel started immediately. What a relief. But, it wouldn't idle. I had set the slides to .5mm lift, it wasn't enough so I increased the idle lift to 1mm. Still not enough. In the end, I had about 2mm of lift on the slides before I got a reasonable idle. That was far more than I thought it should be. Little did I realize this was a sign of things to come.

Because jetting effects are cumulative, you should always start with the idle circuit, move to the pilot jet, the slide, the needle jet, the needle, and then finally the main jet. Right away, I found I had guessed wrong for the pilot circuit. It was far too rich. That's a fairly easy thing to change. Just remove the fuel tank, disconnect both fuel lines, extricate the carbs, take off the float bowls, change the pilot jets, replace the float bowls, install the carbs, hook up the fuel lines, and try again. I must've done that sequence a half-dozen times before I was satisfied.

The next step is slide cutaway, nozzle and needle. I had no replacement parts for these, so if I had guessed wrong here, I was sunk. The slide cutaway affects the transition between the idle jet and the pilot jet.
Fortunately, that seemed to be fine. The nozzle and needle, of course dictate fuel mixture at partial throttle. There's only one way to check if that is in the right range--on the track.

So, with the lower range of carb tuning at least in the ballpark, I headed out for a session on the track. Once on the track, I quickly became puzzled. On the first lap, the bike responded as if it were too rich. The second lap was close, then the third lap seemed massively lean. I headed back into the pits wondering what the problem was.

When I removed the fuel tank and started to remove the carb, I instantly knew I had a problem. I burnt my hand on the carb body. It was raving hot.
No wonder I had a jetting problem. The two carbs were right in the airflow from the head cooling fins, so the super-heated air raised the carb temp far above anything reasonable.

I knew I had to solve this problem, but if I was going to race on Sunday, I also knew I had to get jetting close enough to correct that I wouldn't be spit over the bars. So, throughout the day, I made jetting changes based on the third lap engine response. I reasoned that if the jetting was right with the carbs hot, at least I could start and finish a 6-lap sprint race.
Saturday finally closed with a hollow feeling in my gut that I hadn't solved the problem at all.

In the relative cool of Sunday morning, my brain finally engaged and I resolved to make some sort of heat shield for the carbs. Heat does funny things to your mind, and I hadn't thought about a shield all day Saturday.
So, before the first session, I went scrounging through trash barrels looking for suitable materials. I found a piece of cardboard and snatched it up. A piece of aluminum foil was next. A borrowed pair of scissors, and some duct tape was all I needed. Cardboard shaped with scissors, wrapped in foil, held together with duct tape...I was in business.

The difference on the track was astounding. The cardboard actually appeared to work. The carbs were now dangerously lean. In the paddock, I increased jets three sizes. The carbs themselves were only barely warm to the touch.
During the final practice session everything felt good. I was finally able to try to work out how to ride fast with the new power delivery.

Previously, the engine wouldn't deliver any power above 6,000 rpm. Now, I could run to at least 7,500 rpm (I believe there will be lots more when I actually get the jetting right). This changed all my shift points, and made the gearing too tall. But, it's foolish to make any changes between the last practice and a race so I resolved to not change anything more.

I finished the practice session fairly happy with what I had. But, when I put the Mongrel back on the stand in my pit, I had another sinking feeling in my gut as I discovered the left seat rail had broken. There was an old repair which had finally grown tired and just let go. The seat area was still supported by a triangulating arm, but the piece which broke off supported one side of my oil tank. The last thing I wanted was an oil tank failure. The mental image of the tank dropping its whole load of oil on the rear tire while I was entering Turn 8 at 130 mph was too horrible to contemplate.

My race was the sixth race of the day, so I had a few minutes to work out a solution. I tried to find a broomstick to jam down the broken spar to hold the thing together, but couldn't find anyone who had one. Fortunately, I found an old axle a friend used as a drift which was the perfect size. I beat that sucker into the frame with a hammer and rammed the broken arm over it. Perfect. That was stronger than it had ever been. Finished and ready to go just in time for my race.

The race itself was nearly anticlimactic. The gearing was all wrong, and I had no idea where to shift anymore, but after five months of fighting this project, I finally had a chance to vindicate myself. All those people along the way who said it couldn't be done were wrong. Now, when I whack the throttle open the Mongrel howls and leaps forward in a rush to redline. I'm making a proper heat shield which will allow fine tuning of the carbs without working around heat related problems. And the seat frame is being welded properly. But, for now, I'm basking in the satisfaction in knowing this Mongrel is ready to hunt.

photo by Viewpoint Photography