I've got a completely stock 99 WR400, including the throttle limiter, and I have a problem with the idle surging. Starts, runs fine, but when the engine is hot sometimes the revs jump up for no apparent reason. The revs sound about the same as when it's cold on full choke. Blipping the throttle doesn't do anything - the only thing that seems to work is to put it in gear, let the clutch out to put a load on the engine till the revs come down. Then you can put it back in neutral, or pull in the clutch and it's fine, at least for a while. It happens when I'm stopped and when I'm running it. It's a real pain when you're coming up to a tight corner in the trees, roll off to slow, but the bike just wants to keep going. Any suggestions?? Second is a gearing question. I'm stalling this thing a bit too often and having trouble going up rocky trails - can't seem to crawl smoothly. It's got the stock sprockets and I was considering going to a 52 tooth rear. Is this a good start? I don't want to think about a flywheel weight, at least not now.