[cas3]

before you take anything apart, do a cylinder leak test to see where the compression is going. if you dont have the fancy tool, i dont, you just weld an air fitting to an old spark plug, screw it in, get that cylinder to TDC and put low pressure, like 20lbs to it and listen. air out the carb=intake valve. air out the exhaust pipe=exhaust valve, and air out the oil fill/breather cap=rings. if you get all the same valves, i would suspect cam timing. this one is a puzzler!