Hi Dave.
I have a steady stream of bubbles coming out of the pump/regulator into the line leading to the carb on my 63. The engine is new, with less than 1/2 gallon of fuel through it. There is no air coming from the tank to the regulator, only coming out of the regulator. I have checked to see that all of the screws are tight on items like the regulator, cylinder, backplate, etc. I also replaced the carb fuel line. Fuel is Cool Power 15% with 5oz/gal Klotz added to bring the oil content above 20%, prop is an APC 13x6, turning about 10,700 peak and I'm running the engine at about 10,100 while it breaks in. Regulator screw is even with the bottom of the case now, although I did run it for several flights as it came from the factory, (screwed in about 1.5 turns.) After seeing posts here, I backed it out to where it should be. Any ideas on the source of the bubbles?

Thanks

Jim

The bubbles are normal. If the engine is running OK, ignore them.
The regulator controls the transition from low to high throttle. If it was running OK why did you change it? The flush with the casting setting is just the recommended starting point for setting the reg.
Good Flying,
Dave

Thanks Dave.

Actually, the engine tended to detonate a bit on acceleration sometimes, but not always. Since backing the regulator screw out, it runs perectly at all times. Even though the engine ran well, previous experience made me question bubbles in a fuel line. First engine I've had where this was considered normal. Thanks again...great little motor.

Jim