01 rm80 suddenly run wide open?

[DaveU]

Out riding this weekend with my son, (motocross track) near the end of the day, he stopped suddenly, (one of those where you think your going to have to push the bike back to the truck). He then restarted the bike and returned, when I asked what was up, he said the bike all of a sudden ran wide open on him even when he let go of the throttle. He said it was the second time it did that to him when he was in third gear. I checked the throttle assy, and the cable, nothing seemed tight or freyed. Started up, rev'd and idled severel times back and forth without issue. Where do I go from here? something besides throttle assy cause the wide open issue? Obviously not to safe for my son, I'd like to feel confident in a fix, for his sake.... and mine, if my wife finds out!
Thanks for any thoughts!

 

[2strokerfun]

Sounds like you are perhaps getting an air leak, causing it to go lean and run out of control. Can be left crank seal, base gasket, head gasket (although you normally notice antifreez burning), or oftentimes it is carb boot or reed cage leaking air.

 

[ellandoh]

one grain of sand in a carb jet can cause that also

 

[whenfoxforks-ruled]

I would check the needle for not going up too far, and popping out, bent? And the spark plug! It should help tell if its a lean or other issue, next time it happens? Offer little Johnny down the street ride it? Vintage Bob