xr100 jetting

i have an xr100 that seems to be running a little rich at 1/2 to full throttle. the plug seems to be carbon fouled. i live at 6200' and the temp is 60-80 degrees. the main jet currently is a 90 and the clip is one from the top. the motor and exhaust is stock. the stock air box and snorkel is gone, in it's place is an uni air filter. any ideas or suggestions on the jetting. thanks for any input.

hi there.
hoping you might be able to give a little advice.
i have an xr100 that seems to be running a little
rich at 1/2 to full
throttle. the plug seems to be carbon fouled. i live
at 6200' in north lake
tahoe. the temp is 60-80 degrees. the main jet
currently is a #90 and the
clip is one from the top. the slow jet is a #38 and
the needle, the needle
jet and the pilot jet are stock. the motor and
exhaust is stock. the stock
air box and snorkel is gone, in it's place is an uni
air filter. any ideas
or suggestions on the jetting. thanks for any input.

thanks for the info.

i'm pretty sure it's not oil fouled as i have checked the bore which is within spec, and replaced the rings. it only smokes very slightly at 1/2 to full throttle. the smokes seems to smell a lot like burned or unburned excess fuel as opposed to oil. i have also had the top deck of the cylinder machined and have a new top end gasket kit. the plug also looks to have a lot of carbon deposits as opposed to a wet oily look.

the motor is from the early 1980's. from my research i have read that the needle and needle jet are prone to wear. i have ordered a carb rebuild kit. i am going to give a close look this weekend. i'll pull the top end to see if i have blow by.

the xr100/rm80 conversion, i modified an '86 rm80 frame to hold an xr100 motor. now, i went low budg compared to bbr, dmc and the like, i figure about $1500 total. the reason i did it, my girlfriend is too short for crf150 or any of the other smaller bore 4 strokes. to get her a new xr/crf100, i would have spent more than $1500. for a beginner bike it works well, i just have some fine tuning to do. with this set up she has almost a motocross stance with front disc brakes.