I can't quite understand why the air bubbles. That has not been a problem with any of the Cline regulators that I have run.
Maybe the leak is not in the regulator.

Have been running a Cline regulator on a Moki 210 and the engine performs as well most of the time as can be expected of a model engine. It will idle endlessly, runs hard at the top end, yields good tank time, and would be a perfect setup, except for one thing: this side mounted engine will not run when the plane is inverted. It will quit every time. I have checked the inside the tank mechanics-the feed line moves to the top of the tank when the tank is inverted, the clunk moves freely. Any ideas?