Hi, Had a search but cant find anything along these lines. I just put a high comp piston in my bike, raced it for the first time at the weekend (after a bit of a break in during practice). Bike is stock with exception of a DEP powerbomb header and 13.5:1 piston. 97 Octane fuel. It pulls like a train when the wheels are on the floor and sounds good. The problem I have is when the engine has no load (in neutral or in the air), it doesn't rev out cleanly against the rev limiter, it kind of rev-bog-rev-bog cycles (kind of hunting). Basically I'm happy with it until I need to panic rev in the air, and then it doesn't inspire confidence at all! Any ideas? I was thinking this may be a jetting issue (main jet too rich?). I'm yet to pull the plug and check the colour, will do that when I go out to the bike next.