I see you changed from 10% to 15% nitro. Is the oil content the same ? You may need additional oil. The engine should not get "smoking hot". Another possibility would be a different plug - perhaps an OS #8.

As for the bubble in the line. You may have a piece of crud in the needle valve body. Disassemble the needle valve, clean in fresh fuel and reassemble. Pay particular attention to the "O-rings" on the remote needle valve. There have been several comments about air leaking in through them. If this is happening it would explain the bubble AND the lean run.