Bought a used targa with about 12000 miles. Was barely running when I picked it up. Decided to do a fresh rebuild so I did a top end rebuild with new jug standard size airsal with piston and rings. Only getting 40 lbs of compression. Rings are not broken and piston is in the right way. New reed as well. New base gasket. Tried going back to old jug and even the old piston and getting the same condition which is low compression. Moped will start and run very low idle for about five seconds and quit and while choke is on. We nice the throttle turns the choke off it will rev higher but than die. Was thinking there may be an air leak. Looking for input.