| if it will only run with the choke on it probbly has a air leak , sounds like it could be gaskets or it could be a crankshaft seal
with the headkits some (most) come with a full circle crank
if your not getting a crank included with your headkit you will need to measure the gudgon pin size, they are either 10 mm or a 12 mm pin so u must get a headkit with piston to suit your crankshafts pin & bering size | 
