joco1

i have a omp 540 with a 55ax on it and im having a awful time with bubbles ! I started out with the problem after my first flight so the first thing i did was add a inline fuel filter it seemed to help but after a few flights it got to missing and carrying on and after two dead sticks i always found bubbles in the line! Next i purchased a os bubble less clunk and it really helped the first flight then after the second fill-up it dead sticked again and after looking at the lines i found bubbles again! Next i took off my plastic tie straps on the tank and mounted hooks and rubber bands and half way thru my first flight it dead sticked again and guess what .....i found bubbles in the line AGAIN!! Any suggestions what i need to do now ?

DMcQuinn

My Feedback: (13)

Some bubbles are unavoidable. You may have some other problem. with the tank about 1/4 full, start the engine, advance it to full throttle and hold it straight up for ten seconds or more. while holding it straight up, watch the fuel line going to the carburetor. If there's a stream of bubbles, something's wrong with the tank or plumbing.

If the engine quits when you hold it straight up at full throttle, the main needle valve is too lean. Open it up 1/4 turn and repeat the test.

joco1

so when i check the plumbing what should i look for ,holes in the lines and such, i checked my clunk and it appears to be ok its just missing the bottom of the tank and is moving freely.

Gray Beard

My Feedback: (-1)

Bubbles can even be inside the tank on the main line, if you are using the same bung over and over it can be the bung not seating. To pressure test a tank after you have assembled it just add your main line and a short breather line and cap that off. Fill the sink with water and hold the tank under water and blow hard into the main line and look for bubbles. Pressure testing only shows the outside lines and bung but if you have a pin hole in the main line inside then you will take the tank apart and pressure test the main line buy installing a plug and doing the same thing under water. Filters do not help line or bung leaks.

Villa

Try a brand new Hayes fuel tank. Cut the inside line so you have 1/4" between the end of the clunk and the back of the tank. Replace all of the lines about once per year. Mount the fuel tank on some sort of foam so it is 100% isolated from hard surfaces. I like the rubber bands you are using.

cutaway

The cheap disposable plastic Hanger 9 fuel filters leak air at the seam since the halves are just pressed together and come loose over time. I'm just saying...

When using those, I either glue the halves beforehand with epoxy, or slip a 1/2" long length of large diameter surgical tubing (available at Home Depot in the plumbing department) over the whole filter to seal the seam. Either fix works, the surgical tubing fix will work on an old oily one that has started to seperate.

abaser

Is your tank isolated from the fuse?(Wrapped in foam) Vibrations can be a cause for bubbles also. Ive ran into this before and gave me big troubles until I wrapped the tank. Just a thought.

joco1

my tank is isolated from the fuse im useing 1/2 inch foam

jaka

Hi!
It's simple! If you see bubbles coming in the fuel lines you have a problem! Leaking fuel lines or a leaking rubber expander.
Use Tettra tank and you will no longer have that problem The problem with ordinary tanks is that they use a rubber expander and that rubber expander will sooner or later get loose.

jetmech05

Could it be your high speed needle leaking? Are the bubbles before the high speed needle or after? If you have no bubbles before the needle then the needle leaks.....
However the way you describe the dead sticks it sounds like you may have a line in your tank that leaks...so when the tank is full the leak is submerged in fuel and there fore doesn't leak air...but once you burn down and expose the hole, you suck air lean out and dead stick...
Good Luck

Lnewqban

How well and completely isolated it is?
Any small fuse part or tie-down crushing the foam is able to shake the tank and the fuel inside as to generate foaming.

MinnFlyer

My Feedback: (4)

Replace all of your fuel lines. Don't bother looking for holes as they will be too small to see

joco1

it appears i was just a few clicks too lean i richened it just a little and have no issues now,i still see a few bubbles but it doesnt seem to be a problem anymore......thanks for all the replies!

Gray Beard

My Feedback: (-1)

With today's fuel blending foaming is almost unheard of. A foam wrap used to be a must do when setting up a plane. Once in a while today I will use some foam on the bottom of a tank to raise the height but other then that I no longer bother. You can see this for yourself on any profile plane with the tanks mounted right next to the engine. I even have a site showing how fuel moves around in a tank. It was shot with an on board camera attached to the wing, the tank is hard mounted inside the canopy. Very cool thread, it was a surprise to me to see how fuel moved around during stunts. I always thought the G-forces would keep the fuel in the back of the tank but the video proved me wrong.