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UPGRADING A 1990 SUZUKI DR350S

Updated, January, 1998
Tom Warr
Great Falls, Montana
drwarr@montana.com

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Why take a perfectly good running DR350S (1990) and extensively modify it? Doesn't this sacrifice reliability? Why not just take the money and trade it in on a new bike? Well, the Suzuki has several good points. I wanted to capitalize on the fact that the bike does some things very well, whereas its weak points can be corrected relatively easily, though not that cheaply, with various modifications and upgrades.

The bike is basically sound. It is light at about 275 pounds stock. It has good ground clearance and good brakes, all items that are difficult to correct. It starts easily. And, the seat height is low enough that I can fit on it well, without being intimidated. While big enough for long stints on Interstates, the bike is small enough for real trail riding. Like Goldilocks, I think this bike is just the right size.

For me, a XR600 or KTM 620 is too tall for trail riding. And forget about a BMW, Triumph, Ducati, or similar European dual sport, if I ever stand a chance of doing any serious off pavement riding. Those are great expedition tourers for the LONG haul, but too big and expensive (breakable) for me to ride on a jeep trail. The XR 400 is over $5000 without even being street legal, then add a big tank, luggage rack, etc., and my Project is looking cheaper and cheaper. I thought sticking with the DR was the best bet.

THE IDEAL DUAL SPORT BIKE

The definition should be simple: The most dirt worthy bike one can still ride for extended distances on the highway and carry some luggage. There are two kinds: one that can and one that can't carry a passenger.

Montana is great dual sport country. There are gravel and forest service dirt roads all over the place. I can ride hundreds of miles without seeing civilization. What I need is a bike with speed, stability, range, and reliability. One that can ride on a trail as well as on an Interstate.

LIMITATIONS OF THE STOCK BIKE

1. Power. Stock, it has a flat uninspiring powerband. Not very exciting. And, it lacks the ability to cruise at much over 70 mph. I wanted some top end punch. And I wanted to be able to cruise at 70 - 80 without the feeling I was maxing out the engine for all it was worth.

2. Suspension. Stock it is not bad, but when one tries to push it, one quickly becomes aware of how unstable it becomes. I really wanted a bike with state of the art suspension. From what I read, this just about requires aftermarket components - very few, if any bikes on the market have this in stock form.

3. Tires - the eternal compromise of dual sporters. What I would really like is two sets of wheels, one with knobbies for the dirt, one with Metzler Enduro 3 or 4's for the street.

4. Chassis. The stock tank is too small, with a less than 100 mile range (including reserve), the seat is like sitting on a 4X4, and there is no luggage capacity. Also, I wanted to add some protective items to increase of being able to ride away from a crash in the middle of nowhere.

Any changes had to maintain the bikes good points, especially, good, usable, low end power, easy starting and reliability.

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PROJECT SUZUKI

ENGINE

Several options here. I saw that parts and various options were available from Thumper Racing, White Brothers, and Cycle Gear. I chose CG because they had an integrated kit, and I reasoned they had some experience putting it all together in a way that would still run when all was said and done.

CG has staged kits available, from 1 to 6, each adding more to the one before it. I, of course, not wanting to ever do this again and wanting the ultimate chose stage 6. This includes a 400cc big bore (Cycle Gear told me they didn't recommend going to 435cc at the 10.5 compression because of reliability problems with the stock lower end), hotter cam, racing valve springs, head porting, several mm bore of the carburetor, and high flow air box. They recommend (but it costs extra) some sort of aftermarket exhaust, so I added a large bore header pipe.

I had to remove the engine and ship it (with carb) to Cycle Gear in Richmond, California for the modifications. Shipping was easy. I wrapped it in a garbage bag, and took it to Mailbox, Etc. and for $75 they packed and shipped. Cool.

I had CG put in a new clutch as I had worn the original out (6500 miles).

The engine was shipped back about a month later in a box filled with small pieces of Styrofoam packing. The engine was not wrapped in anything, so those little pieces had all sorts of opportunity to get into the engine, via the intake/exhaust port, and also the holes upon which the oil lines attach. I was not impressed. I cleaned it off as best I could, and changed the oil after the first 100 miles, and sure enough, I found Styrofoam in the oil.

Putting it all together went well. It started right up. It idled so well I questioned whether they put in the hotter cam. Theirs is a 3/4 race version, and not full race, presumably to preserve the low end power curve and also to avoid excess strain on the valve train associated with cams utilizing high and rapid lift.

Initially, the bike ran rough at full throttle, cutting out. I called CG, and they were nice and helpful over the phone. But, it seemed they forgot to send me the extra jets that are supposed to come with the (rather expensive) stage 6 kit. They had installed a 160. I called and bought 4 more jets: 150, 144, 140, and just in case, 165. Sure enough, the 150 has been perfect.

To maximize performance, I guess it is an absolute that the stock muffler needs to be replaced. (Remember not to make yourself unwelcome in the forests full of treehuggers.) I don't know the best choice as to being quiet versus improving performance. I had a SuperTrapp, and didn't like it: too loud, and the exhaust gasses come out the sides of the end of the muffler. That was actually melting my rear fender (about 4" away). I replaced it with a Yoshimura YRD unit, with baffle and spark arrester, which has a better sound, and is not quite as loud.

If I had this to do over again, I would do it again. Cycle Gear doesn't give very good service, as noted repeatedly above (after spending all that money on something they must not sell all that often, I expected the Red Carpet Treatment), but their product works. Bolt it together, and it runs great. It is not cheap, at about $1000, but it works. Second choice would probably be the 435cc kit from Thumper Racing, if one wanted just more low end punch. It is quite a bit cheaper, at about $400. (See May '96 Dirt Rider for details.) Low compression and no mods to the carb should translate to a fair amount of reliability. Full out racers or those wanting the ultimate and who know engines better than me (and can, hence, get the thing to run right) may consider the pot porri of parts available from White Brothers (they could probably offer some good suggestions along the way) that may offer even more performance (like full race cam, biggest bore available, Mikuni flat slide carb, etc.).

SUSPENSION

Forks: Options include replacing them, with i.e. RMX forks, which apparently bolt on (I think one needs also the triple clamps). Too expensive, and I imagine there would be problems with things like the wheel fitting, etc. Dirt Bike Magazine (August, 1993 and July, 1995 issues) has provided details on such a project. Other options include a very expensive (i.e. $2000) Marsocchi fork from White Brothers.

Another option would be to ship the forks and shock off to some suspension specialist to have them revalved/reworked, or whatever it is they do, for about $200 per each end. That would probably be a reasonable option for the fork, but I felt replacing the shock was the way to go, and not all that much more expensive.

I decided to use Race Tech Cartridge fork emulators (about $150). I ordered them through a bike shop in town, and had them install (for about $30). Race Tech fork oil costs about $35 per pint, and 2 are required, so they took it upon themselves to use WB fork oil. I later called Race Tech and they said it really didn't matter, except that RT fork oil lasts longer. Otherwise, viscosity is viscosity.

I replaced the fork springs with Progressive. One had to cut some very cheap looking PVC pipe to make up for the fact that the springs are too short. Following directions, I ended up with too much preload in these springs, with only about 25 mm of sag (supposed to sag about 70 mm, or about 1/3 the total suspension travel.) These are supposed to be associated with great improvements, given their progressively increasing spring rate as the springs are compressed.

Shock: Several companies make aftermarket shocks for the bike. I chose White Power based on their reputation. It seemed to me that most of the nicer bikes and race bikes use them. They are about the most expensive, but all are about the same money. I called Dave at WB and asked which he suggested. Based on the type of riding I do (mostly dual sport), he recommended the White Power Emulsion shock. Cheapest of what they make (at about $550), and otherwise the same except no compression damping adjustment. Fine with me because I would probably not ever adjust it.

To order it, I had to go down to bike shop again and pay in advance. I gave them my weight, and riding skills, etc. (When it came, the preload was set perfectly.) Then, I had to wait 8 weeks for it to be specially built in Holland.

Frame: The stock frame must be very strong, as I have not been able to damage it. However, articles on similar projects in the magazines described modifications to the swing arm. Scotts Performance now sells a replacement swing arm (for about $500) that is probably the strongest. Too much $$, in my opinion. Cycle Gear and Thumper sell a swing arm brace that is welded onto the inside. This is supposed to improve handling by reducing swing arm flex. Thumper was about 1/2 the price of CG for basically the same thing, at about $110. Again, the part is mailed off to Minnesota, then mailed back completed. They did a nice job, all polished up with new decals and looked trick.

MISCELLANEOUS CHASSIS MODIFICATIONS

Acerbis makes a tank that holds about 4 gallons, including reserve. I like the tank, though it is very ugly, it is very tough and has survived innumerable crashes and falls in the dirt. The decals didn't last very long.

Renthall aluminum handlebars are much stronger than stock, and much cheaper than ProTaper.

Acerbis brush guards pay for themselves in protecting the clutch and brake levers, and with the Air Dams, one gets little fairings for the hands that work well to keep your fingers warm.

I bought a stock Suzuki luggage rack, which is nice, but expensive. One available from Cycle Gear is cheaper (about $40 versus $80), and looks bigger in the picture. Actually, what I would really like is a customized rack that would allow luggage to drape over it and clear the hot exhaust pipe.

I got a Chase Harper Tail Trunk which holds a lot and is pretty tough. This is a very functional and utilitarian tail bag with two zippers to provide access to a single large compartment. It stands up even when empty. Relative cheap, at about $30. I am happy with it.

I got some Acerbis lower fork tube covers. Now the bike looks like it is made by Acerbis instead of Suzuki.

I bought a Corbin seat. It is incredibly comfortable, I can ride for hours in comfort. It looks pretty nice, too.

Instrument guard. This in an ungainly structure that surrounds the speedo and tach, and protects against injury in event of a crash. I'm not sure it is necessary: I biffed big time without it, with no damage to the instruments. But, it looks cool, and would provide a place to mount your GPS unit.

I left the stock mirrors and turn signals on. Aftermarket ones are smaller and hence, less functional. I know from experience that the factory ones are reasonably priced if/when broken. When transitioning from street to trail, I have removed the mirrors (using my trusty stock tool kit) and put them in the tail trunk.

I still run stock gearing (14/43), but am contemplating going to DR350 gearing (14/47). For trail riding I just change the countershaft sprocket to 13/43, or 12/43. That is much easier than changing the rear sprocket - I could even do it with the bikes tool kit in the hills. Even with the bigger engine, the bike would not quite pull 15/43.

And finally, I took the inner rear fender off a long time ago, to avoid breaking it. I used the license plate bracket and just bolted it directly to the plastic rear fender. Works fine. I used lock tight on the screws.

I did not replace the pegs with the "Burley Pegs" I hear so much about. Too expensive, at $80, and not necessary, in my view. Stock have been fine.

Finally, I extend my riding season by several months up here in Montana by wearing a Widder electric vest and gloves. Here is what the nice people at Baja Designs say about the DRS's charging system:

The 3-phase stator on the DRS puts out about 185 watts. This is enough to run most electric vests with a wattage range of probably no more than about 60 watts. The Eclipse vest we sell has a power consumption of 45 watts. I do not know what the draw is for the Widder electric vest.

I've never had a problem with a dead battery. I use a thermostat that automatically turns them on and off, thus allowing the battery and charging system to rejuvinate regularly.

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RESULTS

I finished Project Suzuki in April, 1996, and have not had a problem with it, 6000 hard dirt miles later. I am very happy I kept the DR. Again, I marvel at how versatile it is, from blasting across the countryside at 80+, to gnarly trails at <5 mph, it does it all.

ENGINE

I see no evidence of reliability problems. The engine runs great. There is a clearly noticeable increase in low end power, and amazing increase in high rpm power. Smooth power transitions, no stumbling, easy starts, you name it. With stock DRS gearing, I cruise easily at 75 - 80 mph. The power band really gets going above 6000 RPM. The bike will actually light up the rear tire as it comes on the pipe (on gravel roads) IN ANY GEAR. I am very happy.

Power to spare: I wanted enough power to cruise without engine strain at 80+ mph, and I got it. Power deliver is smooth. Low end power is better, and now there is a surge of power above 6000 rpm that adds excitement to an otherwise boring engine.

"Magic Air Box"

The "Magic Air Box" is stage one of Cycle Gear's staged hop up kits, and is included in all the rest of the kits. The air box is shaped like a coffin, with the top completely open. The large, sock shaped air filter is two stage foam - be sure to use good quality foam filter oil, else this thing will not work. There is no question the air flow through this thing is better than stock, it is so huge and open.

On the other hand, it is quite vulnerable to large amounts of dirt that may come its way. The stock air box forms part of the rear fender, and does so by molding perfectly with the rest of the fender, the seat, and the side panels. These separate pieces form a unit to keep the dirt flung off the rear tire out of the workings just in front of it, namely, the air cleaner. The new air box just doesn't fit together with the other pieces as well. For instance, there was a 1/2 inch gap between the rear fender and the air box. This part I had closed with duct tape. However, I failed to notice that dirt could come around from the sides, up underneath the side panels, then up and over into the filter itself. As a result, dirt off the rear tire traveled around the sides of and into the top of the air box, in rather large quantities. Despite using quite a bit of duct tape when originally putting the thing together, I found a 1/4 inch layer of mud in the bottom of that air box!

The other thing that occurred to me as I was doing this was that the opening is still pretty big, and would scoop up a lot of water if the bike were ever immersed - Once, I fell over in a creek. It scooped up water like a bucket, and directed it right into the engine.

SUSPENSION

The suspension upgrades work just amazingly well. It is like floating on pillows.
It took me a while to dial in the front forks, but once done, they give good steering precision and control.

The rear shock seemed perfect out of the box. Power on, over washboard, there was no "loading", or sag developing in the rear end (which would indicate too much rebound damping), while at the same time, the rear tire stayed on the ground and grabbed traction. No tendency to bounce me off the seat (which would indicate too much compression damping (which is not adjustable on that shock)).

The big thing the suspension upgrades did was keep my tires on the ground where they could maximize traction. I was given a very confident feeling, and the ride is very plush. There is no more skittering over washboard surfaces, no bouncing the rear tire (or me) into the air upon hitting unexpected bumps. No headshake. Basically, the rate limiting step is tire traction and rider skill, not suspension.

Riding my friend's stock DR350 recently allowed me to compare my upgrades. I would point out we had very similar knobby tires, with both sets in good condition. The big difference was the suspension. His bike seems to skitter on the surface, and the rear end would fish tail, especially on the very rough surface of the rutted jeep trails. My bike would hold a straight line, and had a very secure feeling on all road surfaces. His front end especially felt like it would wash out too easily. My bike held the tires on the ground while riding on slanted rutted out jeep trails strewn with large rocks. There was no tendency for the bike to kick sideways - it just kept going where I pointed it.

With my DRS400, the Race Tech modified (stock DRS) forks and White Power shock provided rather amazing improvement, and though expensive, IMHO is definitely worth the money if one plans to ride the bike aggressively. For the money, suspension upgrades are more cost effective than engine upgrades. I never thought I could ride the bike over whoop de doos without having the bike bounce sideways, but now it "floats" over them like a (heavy) CR. I can go faster because of better control as much as because of more power

TIRES

Metzler Enduro 4 tires gave me about 5000 miles on the rear. These are good street oriented dual sport tires.

Dunlop 903 DOT legal knobbies gave great traction in all conditions with those tires, but 1200 miles is not enough. That is about one good sized 3 or 4 day weekend ride.

Pirelli MT21 gave less vibration with this tire, than the Dunlop. I guess about the best street legal knobby, compromising performance for mileage. I get about 1500 miles out of rear.

TRAIL RIDING ON PROJECT SUZUKI

My bike does well with lower gearing (13/43) on trails. It is a bit heavy, but using body english perfectly and efficiently will keep the bike moving smoothly. Compared to some true trail bikes, the tighter the trail, the better the smaller bikes went. On the other hand, whenever we came upon a steep hill strewn with softball sized rocks, the other guys would make it slipping and fishtailing, and not very quickly. I wait for them to get out of my way, then I gun it. Sure enough, with 400 cc of high performance power, and lots of $$ in new suspension components (including the swing arm brace), I blast straight up the hill with nary a problem. Cool. Yes, Virginia, Project Suzuki really is an improvement over stock.

ON GRAVEL ROADS

I built the bike for gravel roads, as they are all over the place around Montana. Project Suzuki is now the ultimate back road blaster. It is light on its feet, has great control, nimble steering. Range is about 150 miles +/-, and that could be better. I am always having to detour for gas. A bigger bike might go faster up hills, but I would go faster down them on Project Suzuki. Come out and ride with me, and I will leave you in the dust.

ON THE HIGHWAY

The bike suffers from being physically small. It is subject to cross winds, and has no fairing. It will keep up with traffic, though. The Tail Trunk is big enough for a weekend's worth of clean underwear. As noted, the Corbin seat is really nice and comfortable.

Any questions, please feel free contact me. Thanks for reading, and good luck with your own Project.