Okay I just built my airplane and I am in the process of breaking in the motor. As it runs I notice there are bubbles in the fuel line going to the motor while it is running. Is this normal? It's been ten years since I've flown and I don't recall any bubbles in my last fuel line. Thanks for any help.

Its sucking air from somewhere? There's probably a tiny hole in the fuel line or your needle valve is leaking if the bubbles are between your needle valve and the carb on a remote needle valve engine.

A short piece of fuel line on the remote needle valve threads will act like a gasket.

I concour. You got an air leak. Check where the fuel line attachs to the brass tubing going into the tank. Good Luck, Dave

Okay thanks I'll check out the brass fitting inside of the fuel tank. That's where I thought it might be comming from if it was.

The bubbles if they are coming out of the tank, are originating from a point above the level of the fuel in the tank.

Enjoy,

Jim

The bubbles I usually see are caused by excessive fuel tank vibration.

Hi!
Not likely!
The air bubbles must come from somewhere, and most likely they come from a hole in the fuel lines. Vibration alone is not the culprit.

Regards!
Jan K
Sweden

If your engine has a rear needle valve, are the bubbles you are talking about before or after the needle valve? You didn't mention what engine. If they are in the line between the tank and needle, then all the above is germaine. If they are after the needle, you may have a cracked oring seal on your needle valve assembly.

Trucker. Take a piece of fuel line and suck fuel from the jug. That will eliminate tank and tank line. You can figure the rest.