How much air is normal in your gas line?

[BuzzardChaser]

Engine; BME 115 w/headers and cans on comp 2.6 SX. All finished and ready for the maiden flight but noticed air bubbles in the gas line going into the carb. Air bubbles seem to start at around the tank area. Tank setup 2 line standard with t fitting to medium fuel dot and other line wrapped around tank and vented at bottom. Could not see any leaking or bubbling out of fuel anywhere so just replace all my gas lines and vent line also. Problem still there! Started thinking maybe I have a problem with my fuel dot leaking air so I ripped out my t fitting and went with a 3 line setup where my carb is being fed directly from my tank. another line into my tank with a separate line and clunk to fill/empty and my 3rd vent line I already had. Problem still there! Started thinking my tank was vibrating too much and air is getting into my line inside my tank, so I got a large construction grade sponge and carved out a recess into it and mounted my tank in it and completely isolated my tank from vibration. This installation turned out really cool! But guest what? there still is air bubbles in my gas line! Hey is this normal? How much air is normal to have in your fuel line? I'm getting quite a bit! Help Please! I'm loosing it here!

[flyingklown]

NONE!

[GremlinX]

None is good. When they sit after a flight, the needle will allow some air back in, or even vapor lock will make a bubble right at the fuel inlet nipple at the carb. That is normal, but bubbles in the line while running... no good. With it at a high idle, sometimes a couple of flicks will work the air into the carb and purge the system...

[bigbarper]

Hi, I am using a felt clunk rather than the standard dubro one, supposed to stop bubbles, apparently the Jet boys use them for that very reason, anyway no bubbles in my line.

Good luck.

[AndrewG]

None here either.
Setup is conventional (no felt thingie) cable tied to ply (sponge in between).

Airlock / Air Bubble? (where fuel bypasses it)
Are the air bubbles seen exiting the tank? or only around the tube into carb?
Fuel Filter?

[BuzzardChaser]

This has been a big mystery to me but I finally fixed it. Doesnt make any sense to me why it got fix but now I don't have air in my lines anymore. After trying everything in the book, I finally ordered a round tank from 3W ( I had a square tank from Dubro) Installed it and Bam! no air in my lines! Why that worked, don't know but it worked. I'm sure that my clunk was always submerged in fuel with the dubro tank so even if the tank had a hole in it no air should have entered the lines.

[RollingHarrier]

Glad you got it fixed. Chances are you had a small leak in the clunk line inside the tank or leak in the seal where the line connects to the brass tube on the outside, at least this has been my experience.