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TOPIC: Air bubbles in my fuel line

Re: Air bubbles in my fuel line 5 years 6 months ago #557

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Most problems with fuel supply to your Glow Engine are caused by leaks in the tank or hose.
Even a pinhole will keep an engine from running. Leaks in the bottom of the tank or output hose are obvious as the fuel will leak out, although some small leaks may not leak fuel until the tank is under pressure. Unless the leak is huge it will not effect the running of the engine, however some holes leak air into the fuel line, not fuel out, this is what will cause your engine to run badly. Watch your fuel line with the engine running if you see bubbles in the line you may have a leak or the fuel is foaming. Leaks in the pressure side are harder to find, but effect the pressurization of the tank. Pressure problems can also come from the muffler if the pressure port is clogged or the muffler is loose you can loose pressure.

The best way to check out a tank is to disconnect the hose from the engine and blow through the tank. You should feel very little back-pressure. If you do check for pinched hoses or the pickup hose in the bottom of the tank kinked. Now pinch closed the pressure hose on the muffler and pressurize the tank like you were blowing up a balloon. Now hold the pressure you should not feel any pressure loss. If you do you have a leak. IMPORTANT TIP let go of the pressure hose FIRST, before you release pressure with your mouth or the pressure in the tank will pump a mouth full of the worst tasting cocktail you have ever had into your mouth!!! (Of course if you have ever done this before you already know that.)

Another problem is fuel foaming.
If you have too much vibration the fuel will mix with air in the tank and foam. If this foam gets into the fuel line the fuel mixture will be screwed up. This often happens during a high speed run when the fuel is getting low. It is almost impossible to see this problem on the ground, but if you see bubbles in the fuel line and there are no leaks this may be the problem.
A soft engine mount or padding the fuel tank and balancing the prop may help a lot. An engine that is setup correctly and suddenly stops in the air especially right after increasing altitude probably has this problem.

On your first flight of the year pump some fuel into the tank then shake the airplane. Then pump the fuel out again and discard. You do this to clean the tank up, the fuel and oil left in the tank all winter can turn to goo.

One other problem I had using a small 2oz tank, the fuel hose inside the tank between the clunk and the fuel fitting was so stiff that the clunk would not reach the bottom of the tank it just stuck straight out. I had to add weight to the clunk to get it to the bottom.

To Summarize
  • Either the fuel line has a small hole in it or there is a leak in the tank pick-up.
  • Disconnect your fuel filter and see if that fixes the problem - it may be leaking in air.
  • You may have a suction leak somewhere.
  • If you are using a sintered bronze filter/clunk (pictured) in your tank ditch your external filter, switch tanks, install fresh Dubro fuel line and make sure the tank is mounted in proper padding.


Good luck...
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Air bubbles in my fuel line 5 years 6 months ago #556

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I fitted back my ASP 61 two stoke on my ugly stick. It was running for about two years on electric.
I fitted the tank on foam rubber, after replacing the fuel tubing. The engine is running fine on the ground, but it could quit in the air :sick:
What could be the problem with this stream of bubbles in the fuel line.
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