project yxr100 - info collecting

web site with a conversion... although much more work done to this bike than whats necessary... yxr conversion

Jemco Exhaust - can make a custom undertail exhaust that is suppose to perform very well for $190. puts a 3.5" pipe under seat, modifications to seat or tail section required. hard to tell exactly what those modifications are over the phone.
1919 Blalock rd #B
Houston, 77080
713 461 3834

gearing:
Stuart runs a 16/42 at Katy on his YXR
Peter: 15/42 with ported head that like to rev high to make power. "At the very end of the straight I am in valve float territory for a millisecond, as in no more revs available. I should probably regear to 15/41 or 15/40 now that we're getting a bit quicker in corners, and to save the poor motor. "
15/40 = 0.37 16/42 = .38

from dennie:
I use 15/44 on my YXR with a completely stock xr-100 engine except for:
1 Pipe
2 No air box
3 Needle clip lowered 1 notch
I use 4th and 5th gear only. One of my partners uses third and I'm not sure if my other partner uses third or not.
Note to jbroom: The XR 80 sprockets work on the 100 motor and use stock ysr sprockets on the YXR.

oil consumption advice from dennie:
those engines use a lot of oil. Mine uses a quart of oil in a 6 hour race at Oak Hill. That is slightly more than it holds.

from novak regarding carb:
Hot set up for a "loved on" motor is the ATC 200 carb off of a 4-wheeler.

from Frank:
You will have to file the inside of the rear motor mount a little to get it to fit.

The pipe isn't that bad. I used the clamp from a standard XR exhaust and welded a washer on a piece of 1" tubing to clamp to the head. As for the can, we've been having some fun with that. The last revision is an aluminum bulight bottle, some 1" tubing, holes drilled in the tubing, pink panther insulation from the attick and a little creative welding and wualla, a can. The important thing with the exhaust is to be sure there are enough support points. My biggest problem has been the pipe cracking or falling off because of vibrations.

Clutch cable - you'll have to fab up a bracket to support it. I welded
a support piece off the rear motor mount, I owe you a picture. If you
make the parts to be welded, have the muffler shop weld it for you.

Throttle Cable - I used the entire throttle assembly off an XR.

CDI, etc. - Pretty self explanatory. I would also use an XR E-Stop
button arrangement as well.

Motor Mount - Denny has that covered for you.

Exhaust - Muffler shop sounds like as good a solution as any for the
short term. We broke a lot of pipes off at the flange because we didn't
have any support for it. Be sure it is properly supported and support
it ONLY off the motor, not the frame. I'll send some pictures of what I
did to try to help the problem, but even Saturday I had to weld the pipe
back up again. It has been a real problem for me. It's not perfect,
but it works.

Intake manifold - The stock XR intake manifold kicks the carburetor over
close to the frame. It is difficult to arrange the air filter because
the frame gets in the way. Kelly Tomkins machined a nice intake
manifold for me that runs straight in. I think we had it running with
the stock unit in the beginning, but the KT unit is a lot easier to work
with. I'll send you a photo. You won't need it to run, it just makes
things a lot nicer.

Gearing - I'll send you the gearing that we run. If I remember
correctly, we use a 420 chain and sprockets. Just get an XR80 front
sprocket and you can use the existing gearing you have if it's the right
count. I think I use 16:44, but I need to make sure.

Shift Leaver - I'm not sure where I got the shift lever we used from.
I'll send you a picture, it may have come from the XR but turned
backwards. It will shift GP, not regular.

Everything else is pretty much bulk standard YSR stuff. Be careful with
the XR motor you buy. We bought 2 of them and they needed some love. I
think one we were missing a flywheel and pick up and the head and cam
were trashed, and the other had problems with the cam. Getting an XR
motor for around $200 will mean you need to do some work to it.

power info:
http://www.4strokes.com/tech/honda/cheapxr1.asp