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Air Buble in my fuel lines

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Old 08-15-2012, 05:52 PM
  #1
LEO77
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Default Air Buble in my fuel lines

Hello everyone,

I have purchased a new plane and using on it an OS .61 fx.
I have recently noticed that there is a lot of air between the needle valve and the carburetor line. I have proceeded with changing all my fuel lines and the fuel tank with no luck and the problem still persists.

I did put foam padding under the fuel tank to minimize the vibrations and no luck.
right now the plane is grounded cause I had 2 dead sticks due to this problem.
I ordered a new o-ring for my needle valve, may be that could be the cause as well.

Have you had any similar problems and what was the fix?

regards
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Old 08-15-2012, 06:13 PM
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Charlie P.
 
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Default RE: Air Buble in my fuel lines



You did what I would have done - replace the pick-up line in the tank and the tank to carb line. 

You are using a pressure line from the muffler to the tank?

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Old 08-15-2012, 06:35 PM
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Default RE: Air Buble in my fuel lines

I fought this exact same problem with my FX61. I replaced needle valve O ring and the banjo seals. Nothing worked. I solved it by buying a remote needle valve and bypassing the OS one. I used a Jett needle, but any remote needle will work.
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Old 08-15-2012, 07:43 PM
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Default RE: Air Buble in my fuel lines

Quote:
ORIGINAL: LEO77

Hello everyone,

I have purchased a new plane and using on it an OS .61 fx.
I have recently noticed that there is a lot of air between the needle valve and the carburetor line. I have proceeded with changing all my fuel lines and the fuel tank with no luck and the problem still persists.

I did put foam padding under the fuel tank to minimize the vibrations and no luck.
right now the plane is grounded cause I had 2 dead sticks due to this problem.
I ordered a new o-ring for my needle valve, may be that could be the cause as well.

Have you had any similar problems and what was the fix?

regards
How does it run on the ground, and how do you know the bubbles caused the dead sticks? My point is that air bubbles in the fuel line would probably prevent you from setting your engine appropriately rich on the ground long before you took off. But I have seen air bubbles in fuel lines on several occasions and in some instances, experienced no problems with setting the needle valve. If I can set the engine rich enough on the ground, I probably don't have a problem.

Kurt
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Old 08-26-2012, 05:07 AM
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im_a_rcav8r
 
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Default RE: Air Buble in my fuel lines

It is not uncommon to have air in the line between the needle and the carb however; too much air can be a problem.  Thinks for you to check.

1)     Be sure your pressure line (the brass tube) inside the tank goes to the top of the tank.   The line should be out of the fuel so it does not blow bubbles in the fuel.

2)     Be sure your pressure hose is attached to the pressure line on the fuel tank not the vent/fill line (if you use a 3 line system.

3)     Be sure the line between the needle and carb is not split.

4)     Be sure the o-ring on the needle is in place

5)     Be sure the nipple fittings between the fuel tank and the needle are tight and the gasket is in place.

6)     You can use extra fuel line on the pressure hose (about 6 to 10 inches) coil it up and use twist ties to keep it neat.  The extra line creates a buffer between the fuel tank and the muffler to smooth out the air going into the tank.  It makes the air more constant and gets rid of the puff puff puff effect that can sometimes cause problems.

7)     If you are getting air bubbles in the hose between the tank and the needle you may have a split in the brass tube in the tank.  With a full tank of fuel hold the plane nose down so the fuel covers the brass tubes.  If the air goes away I would look there.

Good luck

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Old 08-26-2012, 05:19 AM
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Default RE: Air Buble in my fuel lines

If you are using any of the refueling valves, by pass it and try agine.

John
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Old 08-26-2012, 07:55 AM
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Default RE: Air Buble in my fuel lines

I agree with John and RC...if you have a leaking fuel valve it would cause bubbles but you'd see the bubbles before the needle valve...a tuned engine with bubbles in the fuel line is an engine tuned to the fuel that is available. As long as the bubbles don't get worse in flight. The needle valve has the range to compensate for small bubbles....Try richening the high end an 1/8 of a turn and fly until you can replace the O ring
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Old 08-26-2012, 11:33 AM
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Default RE: Air Buble in my fuel lines

This was 10 days ago and Leo hasn't been back. He posted the same question on RC Group. I really wanted to know if he had a filler on this plane or not? I forgot all about them these days, the word has gotten out over the last 10 years and I don't see them often so I tend to forget about them.
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