Well Gyro I had the same problem with my engine, I started a thread about it. I was advised many things, first thing, that when engine is running good on the ground without being nose up, you need to run it on rich, once engine starts running to max rpm, and it kinda coughs then turn needle valve back few clicks, and check transition 2 to 4 times then lift nose up. Infact what I was told that I was running engine lean, so I ran it on rich, though finally I found out the carb was the problem and taking air, still problem persists due to loose carb, Im gonna get another carb, my engine is HB 61 2C. I checked all the fuel lines, fuel line connected to the clunk, re-adjusted the position of fuel tank litter higher than carb nipple, now it atleast runs good but waiting for the carb. Check the carb, check the position of fuel tank, run it on rich, I hope it would work fine, im just very short experienced guy, Im sure a lot of well experienced guys would put in their advices to resolve your matter.

Good Luck

Mody