I don't know if this helps you any, but I've had like 25 or 30 bikes, and out of all of them, the one that would four cycle the worst just happened to be the only trials bike that I ever owned (not the same brand as yours). It ran great otherwise. I'm wondering if it is aggravated by the large flywheel, low porting, and smallish carburetor. Could it just be the nature of the beast? I haven't ever been to a trials competition, so I can't say if this is normal...