Some two years ago I bought a MZ 500 R Tour, also known as Saxon Tour, also known as MuZ etc. Until that time I rode an XT500, but it had too many little problems to be called a reliable every day machine, especially since I had to use it an the dark a lot. So, I was told the MZ's were reliable, had rather cheap parts (not cheapy ;-) and an indestructible Rotax engine. Boy, was that right. I had to change a front light bulb once, and that's it for two years.
Downside was, the bike wouldn't pull as hard as the XT, and it's sounded like a wet fart. The latter was solved easily by knocking over some barriers in the exhaust pipe. But still, it didn't have much power: top speed was around 140 kmph, sometimes with strong wind I had to shift back to 4 to maintain a mere 120 kmph. And wheelies where only possible with the aid of the clutch or the front springs.
Handling was very good though: on a tour with some 30 other bikes on little narrow roads, only a few BMW 1100 GS's, one old Bol d'Or and me were in front, the rest couldn't keep up. It's a light bike with good gear and excellent front brakes, and it can really be tossed around. But acceleration remained poor.
I than fitted a Supertrapp, and changed to a bigger main jet. I also removed the lid from the airbox, and the perforated paper from the air filter. Now it sounded really awesome and seemed to pull better. But it's never enough once you start ;-)
Next plan was quite ambitious, and couldn't be done by myself: I was really gonna release the power that had to be somewhere, but not over the top. I consulted a local tuner, who has a wide experience with these engines: he had cranked them up above 72 bhp at the rear wheel. But those where for racing and could easily break. Still, he knew what he was talking about. We decided to do the following:
- Port and polish the head
- Build and fit a wider outlet manifold
- Get bigger inlet valves
- Change from 89 to 97 mm piston, thus increasing from 500 to 590 cc
- Fit a 40 mm Dell Orto instead of a 34. No acceleration pump, as he felt it was only hell to tune and had little to none impact.
- Off course the Supertrapp.
- Change the paper airfilter for a K&N filter, hidden in the airbox.
- Work on the camshaft. This really is a special job. Since a new one would cost some $300 in Holland, he modifies the old one. Instead of raising the cam which is almost impossible, he lowers the cylindrical part of the cam, thus getting a cam with the characteristic of a crosser: lots of low end power, which is what I wanted. This only costs $80! (Hey, I'm dutch, we've worked ages to earn our name!)
Now for the payoff.
Before, maximum power was about 28 bhp @ 6000 rpm measured at the rear wheel.
Maximum power now: 42 bhp @ 7000 rpm
Maximum torque was 38 Nm, and >35 Nm @ 3200 - 5200 rpm
Maximum torque now: 50 Nm, and > 45 Nm 3200 - 6500 rpm
The graph shows it all. In fact, two figures are shown for the current state, one with the filterbox and one with a completely open carb. The latter has more top end power, but less low end.
Performance is great now. Although I don't have any figures, it pulls very well, and vibration is a lot less then, say, a Duke.
The bike still has it's 110 rear wheel and 90 front wheel, which isn't a lot, but provides excellent handling. Bigger tires would mean I had to remove the chain tunnel, and besides the fact that for maintenance reasons I want to keep them, I also like the bike to look original, to really surprise big supersports. And the smaller tires give better handling too. So, no flashy windscreen, no superbike handlebars and all that. The only concession I had to make is the Supertrapp exhaust, and I want to fit steel break lines. But for now, I'll just enjoy my new bike and drive it savely through the winter
Pom Bleeksma ( pommetje@raketnet.nl )
12/18/99