How long has it been since you've checked your valve clearances? I don't believe it has anything to do with a thermostat, and I doubt your electronics are to blame, either. It could also be a vacuum tube that is getting soft and kinking off when it gets warm.

FIRST thing I'd check is the vacuum and vent hoses. If they are OK, I'd go to the valve clearance.

 

i never have checked them. I havent checked vacuum tubes either. This has been a gradule problem that has gotten worse since about 9 months into owning the bike. I had it to the dealer then when it was under warranty but i don't think they got it warm enuff then to experience it. Now it only takes about 10 minutes in this warm weather. I'll find out how to check valve clearance and check my vacuum tubes as well. thanx for all the suggestions everybody!

 

I agree with the valve clearance part. I have a '09 and when I did my 351 conversion not long ago (runs great, by the way) I also decided to check valve clearances while everything was opened up. Glad I did. Found that one exhaust and both intakes were right at the tight ends of the tolerances. The way these bucket and shim arrangements work, they weren't gonna get any looser as time went by. Went from 3.1 shims in each position to 3.05's. Hopefully I put off any valve clearance problems for a little while by doing this.

Like mine, maybe your bike came off the production line a little to the tight side of the tolerances and now the effects are finally showing up?

 

BTW, the reason I'd check the vacuum and vent hoses first, is that they are so easy to check. I'm betting it's the valves going out of spec.

 

OP - I have a 1979 Honda trail 50 that had the same issue. It would start up fine, run perfect the first five minutes until it got hot, and then it was done with. It wouldn't fire up and would only run if I had the throttle near wide open.

At first I thought that it was a jetting issue but as it turns out it was a valve clearance issue.

 

My XR500 did the same thing. Popping and running like crap when hot. Adjusting the valves worked on that ride.

 

Hi there,

I'm running (or not) into the same problem, i always had issue. It degraded this year.I purchase a new rectifier\regulator,waiting for it in the mail, but as the bike warms up the current stop flowing threw until there is not enough current provided to run the beast.I'll let you know if it really does solve my prob.

 

There is also a ground issue with the electronics piece everyone is talking about, it's symptoms were more of a high speed miss but if it was allowed to get worse it could present as a non running issue. The fix was to add a ground wire. I haven't had any issues myself so I can't be any more specific about this mod.

 

i bought my bike brand new and it started with in 5 or 6 monts after i bought it with less than 200 miles on it. It still only has just under 800 now and it has progressively gotten worse with miles. Please let me know if that works for you. I really dont wanna tear the head off to check valve clearance if i can avoid it..lol! thanx!

 

i'll keep this in mind as well. thanks!