I have a grubee slant head 66cc engine with an NT carb, and an expansion chamber with that silver silencer thing on the end. Basically my bike boggs and has almost no power, it is VERY jerky and will not reach top speed. This all happened out of no where too. I cleaned my carb and adjusted my needle to the leanest possible setting. I also cleaned my filter and tried running with it off as well. My plug still comes out black, oily, and wet. It seems like not enough air is reaching the engine. I tried running with the expansion chamber completely off for a couple of minutes and no difference (except now I'm deaf lol). My spark plug sparks just fine. I am out of ideas.