here's a tip. if your engine starts up and runs smooth at all rpms, even tho its lacking power, your spark plug is fine. now, back to my original question, HOW MUCH COMPRESSION DO YOU HAVE? you installed a performance exhaust, and didnt upjet. so you have been running dangerously lean. chances are your piston, rings, andcylinder are worn out. compression on a 2 stroke is VERY important. you need to have 120 lbs or higher to run correctly. anything lower and it wont run worth a damn.