I had very good luck with mine AFTER a slight mishap.
Same problem you noted... rough idle, bad transition, and I couldn't shut the engine down with the throttle... all of the signs of an air leak.
The mishap was when I smacked the prop on the takeoff roll. It still sounded fine so I continued and flew. After a few minutes, I found that I had no throttle response... I was flying an Aircore Colt-40 on this power-monster at full throttle and had to do so until the engine died
Upon landing, I found that I had lost one of the prop tips, and the OOB situation had vibrated the barrel partially out of the carb, which became jammed against the stop screw.

Quick work with a file got the barrel working again, but at this point, I went through the carb-to-case joint and the backplate joint and sealed them with silicone sealer... I think I actually used aquarium adhesive (it's all I had 200 miles from home and 100 miles from the nearest hardware store).

I couldn't believe the difference. The engine tuned in wonderfully, shut down with the throttle, and never gave me a problem again.