Bubbles from my nitro engine's needle valve?

by Mike Rogers
(Beaconsfield QC)

Tiny bubbles are appearing between the needle valve and the carburetor of my engine.

I have checked for tubing leaks, and diddled with the high speed mixture needle valve and it does not seem to affect the bubbles.

Should I just replace the needle valve?

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Bubbles from my nitro engine's needle valve?

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Sep 03, 2009
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kinda sounds like a leak at the needle valve...
by: Matt

Hi Mike,

So there is no bubbles from the needle valve to the fuel tank, but there is bubbles from the needle valve to the engine's carb?

Vibration of a glow engine's fuel tank is a common source of bubbles in the fuel line between the fuel tank and needle valve. This is why most kits and ARFs recommend that you wrap the tank in foam to dampen the vibrations.

But if the bubbles are only appearing after the needle valve, and not before, it does seem that air is being introduced into the line at the needle valve.

How long has this been happening? Is this a new engine? Or is this an engine you've had for a while?

Have you had any "rough" landings lately?

Before replacing the needle valve, take a good look at the nipples on the needle valve assembly that the tubing connects to. Make sure they are screwed in tight and not cracked or damaged.

Another test would be to run a short run of tubing on both sides of the needle valve. Blow into one side while pinching the other side. If there is a leak you maybe able to notice by performing this test.