there probably isnt anything wrong with the engine, it DID run great before, 99% of the time it a fuel problem. among many other things to check, fuel tank, and lines, junk in the carb, etc....air could be leaking around the needle valve too. remove the needle valve and push a 3/16" long peice of fuel line over past the threads, install the valve and make sure that little peice of line covers the area that could suck air into, the original o-ring usualy leaks after a while