How about clean your clutches, get fresh clutch springs and a new belt with proper deflection before you start hacking into things.So I bought a 2003 ZL600 efi (with power valves of course) at the beginning of the season; it runs beautiful except recently it has started to bog out at 3000 rpms from a stop when you give it full throttle. If you ease into it its fine, even it its a bit aggressively. I've looked around and it seems like forums are saying its the apv servo and that its common, however I don't want to just start replacing parts so i figured I'd ask all of you that have more knowledge of the subject. I'm not familiar with sleds at all as far as working on them, this is my first snowmobile that I own and have to maintain lol so bare with me. I haven't cleaned the power valves or done anything due to not really knowing for sure where to start.