Sounds like you definetly have air. I got a tip from Rossi. Take HI temp RTV, and spread it on the carb. Push Down while tighting the carb in place. Tighten all screws on the motor. There is on most motors a nut that hold the hi end needle in place on the adjustment. You can have air there and really not know it. Look close, and if you see as much as a drop of fuel tighten it as well. Be careful not to over tighten. Also the back plate is a area that can cause air. The tip from Rossi is a good one. Now I do this to all my engines. I have a 15 that has a crack on the motor wnere the carb goes. The RTV even stoped that from getting air.

Good Luck