I had an issue with my carb on my Big Bear 350. It would only run with the choke pulled out. I figured it was a clogged jet, so I removed the carb, disassembled, and put a kit in while it was torn apart and cleaned. When I re-assembled the carb, I set the adj screw to the same amount of turns as the original, and things were great. But, when I started it the first time, I opened the choke to the first notch, and it caused the engine to rev to a high fast idle immediately. I pushed the choke in all the way, and it ran great, but noticed it occasionally backfiring. I thought the adjustment screw on the bottom of the carb needed tweeked, so I screwed it all the way in gently, backed it off 2 turns, and tried to smooth it out. It seemed to smooth out a bit, but still backfires occasionally, and when starting while cold with the choke out, it still goes to fast idle immediately. Anything I am missing, that I need to address, or do I need to keep trying to tweek the adjustment screw? I didn't know if a vacuum leak would cause this problem. Any help would be appreciated.

 

There are quite a few little passageways in a carb which may not be clear.

Did you make sure the float height is correct?