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Bubbles in fuel

Old 04-11-2007, 02:00 AM
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riteflyer
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Default Bubbles in fuel

Have just come across a problem with an ARF ultimate bipe that I was about to test fly.At full power quite large bubbles could be seen in the fuel line to the carby.At low power it seems to be clear. The engine still seems to run fine with the bubbles . What I have done so far to cure the problem is: All fuel lines have been replaced and an extra piece of fuel line added on top of the fuel lines to act as a form of extra clamp,checked the clunk and fuel line for length,checked the rubber bung for leaks,balanced the prop, but the problem is still there. Being an ARF I cannot put foam around the tank to prevent foaming in the tank unless I start cutting away formers in the fuselage.
Does anybody have any other thoughts about a cure? Also the engine is mounted at 90 deg. and fitted with a pitts muffler.
Old 04-11-2007, 08:56 AM
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broke_n_bummin
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Default RE: Bubbles in fuel

make sure your vent from the exhaust is above the fuel line
Old 04-11-2007, 12:18 PM
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snys
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Default RE: Bubbles in fuel

I have a stick that does the same thing. I swapped tanks, same thing. Then I swapped engines (I have two OS .50 SX engines) problem remained.
Foam around the tank lessened the problem, but I still see some bubbles. I think more foam (or maybe better quality) will cure it.

This is only a stick, so I am not too particular about it.
Old 04-12-2007, 07:44 PM
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Default RE: Bubbles in fuel

vibration causes foaming since you can't add foam only thing I can think of is a soft mount engine mount to isolate the the vibration from the aieframe.
Old 04-12-2007, 09:24 PM
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chashint
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Default RE: Bubbles in fuel

Idles good ?? yes ?
Transitions from idle to full throttle good ?? yes ?
Good RPM at full throttle ?? yes ?
Don't worry to much about it and have fun.
Old 04-12-2007, 10:53 PM
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sebo
 
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Default RE: Bubbles in fuel

I read something recently that may or may not work.
It was stated that a couple of drops of Armoral (the kind you use to clean your car dash board) added to the fuel will stop the foaming.
I haven't tried it. Has anyone else?
Old 04-13-2007, 03:55 AM
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riteflyer
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Default RE: Bubbles in fuel

Thanks everybody for the info.Will try your suggestions and get back to you.
Old 04-13-2007, 05:50 AM
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BillS
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Default RE: Bubbles in fuel

My experience indicates that bubbles in the fuel line will cause the engine to shut down at strange and unusual times usually damaging the airplane.

Being an ARF I cannot put foam around the tank to prevent foaming in the tank unless I start cutting away formers in the fuselage.
I would do whatever necessary to put latex foam around the tank, smaller tank, trim the formers, or dual tanks. If you don’t fix the air bubbles the airplane will not live long.

Bill
Old 04-13-2007, 09:28 PM
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riteflyer
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Default RE: Bubbles in fuel

Have tried everything except a soft mount .Looks like it maybe next. l

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