03 YZ450 Low on compression? New to 4 strokes.

The story: I've bought a yz back in October for a nice 400$, in remarkably good condition. Has a high comp piston kit, acerbis XL tank, and suspension already set to me. Only had carb problems, and the fact the shifter oil seal is pinched a bit to where it drips a little.

So what I've done to it: cleaned the carbs, put a new hot starter billet and plunger in the carb since they where both snapped and dethreadded, had to redo the right side crank covers gasket after it blew it, leaker oil tremendously, and just rode it around a fair bit. Probly between the range of 10-20 hours, maybe 3 of those hard use on a MX track (keep in mind, bit of a beginner, so I was not really forcing it like a pro. Couldn't even clear a table top hahah) the rest being rode around a bit fast on trails. Gently used compared to most MX bikes

THE PROBLEM: When I got the bike, it seemed to be unbearable to kick. Onnce the compression stroke was hit, the entire bike would Bob trying to get past it. Now in the present, its equivalent to my 250 2stroke that puts out 180 psi flat in the required kickingforce.

THE ACTUAL DAMN QUESTION: so could it be just the hi comp piston kit breaking in? The prev owner( trust worthy and true, close friend of mine for around 7 years) said it didn't have many hours on the new top end, especially since he moved after rebuilding the bike and rode it little. Keep in mind as well, the bike still has the stupid amount of torque and power from when I first got it runnning

Any other little bits and pieces of help about this bike would be awesome BTW, kinda new to it.

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now