Hello folks, I recently bought an 82 yz490 to race in the classic grasstrack over here in Northern Ireland. The bike went well apart from being quite a pig to start but now it seems she wont sart or run. The spark is strong and so is compression. I lifted the head off and noticed alot of detonation around the outer edges of the piston crown, the cylinder dome also shows signs of detonation. I've heard these motors are prone to detonation even when jetted correctly so I can only assume the ignition timing has slipped out of sync with the crank. Has anyone any thought? i havent yet pulled the flywheel off. I cant seem to find much info on timing these motors so any help would be greatly apreciated.
cheers
Dee
cheers
Dee