Club car running rough

Ok I have a 99 club car 350d single cylinder..

Problem is.. Runs Rough full throttle.. Spits And runs like crap, back firing..

Runs ok with just a little gas.. but it's starts spitting and popping when you give it more gas.. I have a new coil, carb, fuel lines filters, spark plug, air filter,oil .. I've done replaced everything I can think off.. To a single cylinder engine I can..

I haven't pull the flywheel yet, I had some tell me about a aluminum key that can break or bend.. Goes on the crank to the flywheel.. Can throw the timing off just a little..,

I'm just wondering if I have a bad engine.. It's has been over reved by the previous owner..

It was running fine .. Just one ride and it started running rough.. I'm just looking to see what steps I should take from here to test..,because I'm lost..

Any and all comments much appreciated..