Check all your fuel lines, filters , tank, clutch etc first to try to isolate the problem and eliminate other suspect areas beside the actual engine.

Then on the engine Check seals, o rings, bearings, rod etc...

If it gets to where you are stuck, send it in to us and just pay for shipping charges and we will inspect it for you and let you know exactly whats going on. We wont charge for the inspection.

Hope this helps,
Lance
RcRenew.com