Bob - You've got a great engoine there. It'll sereve you for many uears when properly cared for.

Rudeboy is correct about the air leak and chances are it is leaking around the carb mount, needle threads, or back plate. I would coat the carb throat (outside) and backplate o-ring with automotive axel grease. and install. Take care not to roll the o-ring on the back plate when insterting. Insert this plate using a twisting motion (small amounts of CW and CCW) until seated. If you are still having the same problem, then place a small length of fuel tubing over the needle valve and seat, as the air is most likely entering through the needle threads.

Good luck and let us know how you fare.