I purchased a 2005 recon yesterday. They said it needed a new carburetor. I get it home and pulled the carb, fuel tank, fuel lines and completely cleaned whole fuel system. Go it started but will only start and stay running on full throttle. Sounds terrible. Popping out the exhaust and noise in the motor. Sounds as if it has compression lost. Any pointers would help. It's a lil project with my son so it makes it important to get it fixed. Should I rebuild the top end? Thanks!

 

Do a compression test, anything over 90 psi is OK if the piston isn't slapping. If compression is down, check the valve clearances, they should be about 0.006". If the compression is still low it is time to think about a top end rebuild.

 

I checked the compression last night, it was a lil bit over 100. Ran it for a few then killed and wouldn't start. Done a compression test today and I'm at 60. Put new carburetor and spark plug. I pulled the top end tonight and it's very clean and looks really good. I will measure the clearance tomorrow and start all over. Thanks for the response, advice helps. And this is my first one I jump into.

 

While it was running I also heard something slapping in the head.

 

If there was noise coming from the top end, something must be wrong. Check the gudgeon (wrist) pin for seizure, and the valve seats, although I haven't had a 250 do it, I have had lots of 350s with loose seats, they make a loud tapping noise.

 

Thanks! I will check it tonight. I'll let you know what I figure out. I need a repair manual cause I have a feeling I'll have to rebuild it.