XR100 overheating?

HiG4s

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#1
My son's XR100 seems to be overheating. We rode yeasterday and it was fine for a couple of hours, riding about an hour and taking a break each time. Then it just quit. He was practicing around an MX track. He pull under the tree in the center of the track and by the time I walked out there he had it running again. He road abourt 20 minutes and took a break. Later he went out and after about an hour of riding, some in the trails then back to the track it quit again. I pulled the plug, it was black with some small white spots. I let the bike cool, check the carb for dirt and put in a different plug. I worked fine again for an hour and a half or so and again quit. By then I was time to leave and I haven't looked at it since. Anyone else have this type problem or have any ideas.
 
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#2
I don't think it's overheating. If the plug is black, it's running WAY too rich. I know it sounds basic, but make sure the air filter si clean and not clogged. I would also check to make sure the float is not stuck or something is not in the inlet valve atached to the float. Those little 100's are about as reliable as a hammer and overheating would not be one of the problems that they are plagued with.
 

Boit

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#3
Did you notice any smoking while riding....or, especially when first starting it after it quit those times?
 

ACS

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#4
If it was the plug it would die completly and not restart until you replace the plug with a new one. Most XR80 /100 run pretty black sooty plugs standard for years. I note you changed the plug and it went but it went again the first time after it had cooled.

One thing to try is to check the valve clearances. They are possibly too small. If its been on a MX track they tend to get reved harder than the normal thrashing they get and the valves esp the intake start to mushroom or hammer the seat. Eventually no valve clearence when its hot but as soon as it cools a bit its going again as. Check the clearences and try the valve clearence at maximum spec. Hope that helps.
 
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#5
Which position is the needle in? Mine runs hot, and I found since I leaned it out a notch on the needle it runs way better. Also, make sure the cam chain is at the correct tension and the valves are correctly adjusted. Was the oil changed recently? My 100 used to be very bad but now after a complete top end rebuild and adjusting everything, it runs great. Oh yeah, don't hold it pinned all the time, as this will contribute to overheating. I usually ride in a gear high and use the low RPMs.
 

HiG4s

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#6
I tried to start it and it just wouldn't run right even cold now, but seemed better with the choke half on. So I pulled the carb and cleaned it, didn't really find any dirt. And cleaned the air filter, it didn't seem that bad. After I put it back together it seemed fine. I know the air filter has twice as thick of foam with smaller holes than the filter on my 125 2-stroke. So I suppose it clogs much eaiser. Does anyone make a more performance filter for the XR100?
 

Offroadr

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#7
I don't think there is a way to overheat an XR100. We ride them HARD!! Ask AJ:D We weigh twice what they are supposed to handle and they rarely see less than full throttle. Especially on the flattrack or grasstracks we play on.

I have removed the airbox and run a Uni filter. It fits directly on the carb. I have used it for 2 years and have no problems.
 
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#8
I suspect the problem will come back. I don't think it was the filter, if it wasn't that dirty.

Check the valves, adjust them. It should be done every year or so anyway.

Is this a points or CDI model? If it's points, replace them and the condenser.