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Air bubbles in fuel line ?

Old 05-16-2007, 08:52 PM
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Hobie
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Default Air bubbles in fuel line ?

What causes air bubbles in the fuel line ? I have been breaking in a new Magnum XL .46 which I have running ok I guess but with the air bubbles it is hard to tell . How do I fix it ? The Magnum is on a Sig Somthin Extra that was given to me never been flown .
Old 05-16-2007, 10:14 PM
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Default RE: Air bubbles in fuel line ?

It can be from different things. You could have small holes in the fuel lines in the tank. The stopper in the end of the tank may not be tight enough and it can draw in air there. Some filters leak air. (not sure if you have one) I use the type of filters that don't come apart and it eliminates air leakage. I would start by replacing the fuel lines in the tank with new fuel tubing and then check the lines or replace the lines that are on the outside of the tank going to the carb and muffler. It could even have a hole in the tank it's self. Sometimes tanks can rub on the fuse framing and wear through or people drill into them when installing hardware. [8D]
Old 05-17-2007, 07:05 AM
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Default RE: Air bubbles in fuel line ?

I am betting that you have a bad fuel line. You may want to consider changing the fuel line from the tank to the carb. Also as mentioned, check the stopper in the tank. Good Luck, Dave
Old 05-17-2007, 08:22 AM
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Default RE: Air bubbles in fuel line ?

Before you try to fix anything, let's try to find out if there's a problem.

Lots of guys say "I have bubbles in the fuel line"

Ok, so we ask, "How big are the bubbles?"

And the answer is, "Tiny"

Well, obviously you can't fit a big bubble in a fuel line, so "Tiny" is not the best description.

So let's analize a little further...

When the engine is running, do you get (Referring to the picture):

Fig. 1 - A small amount of foamy bubbles the pool to the top of the fuel line and either remain still or move very slowly.

Fig.2 - Asteady stream of tiny bubbles the flow with the fuel

Fig.3 - A LOT of bubbles that move rapidly with the fuel
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Old 05-17-2007, 09:31 AM
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BillS
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Default RE: Air bubbles in fuel line ?

In my experience bubbles in the fuel line is almost always fuel foaming. The tank can be packed too tight, or against the structure, or no foam, or the wrong kind of foam rubber.

Bill
Old 05-17-2007, 10:21 AM
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Default RE: Air bubbles in fuel line ?

Actually MinnFlyer none of those examples . It's more like intermittent voids in the fuel flow rather than bubbles . The fuel can be coming through nice and smooth then all of a sudden you can see 2 or 3 air pockets in the line of course causing the engine to hesitate then the fuel will flow normally again for a little bit before it does it again . I just got up a little bit ago and have not looked at the tank and fuel lines yet . My weekend is over with no flying [&o] I go back to work tonight and with 17mph winds gusting to 27mph I will not fly again .
Old 05-17-2007, 10:26 AM
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Default RE: Air bubbles in fuel line ?

Ok, that (to me) is an indication that there's something wrong inside the tank. Maybe a split line, or a stuck clunk.
Old 05-17-2007, 12:58 PM
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Default RE: Air bubbles in fuel line ?


ORIGINAL: MinnFlyer

Ok, that (to me) is an indication that there's something wrong inside the tank. Maybe a split line, or a stuck clunk.
You may be right . I looked at it a little bit ago it needs foam for sure . It is going to be a real @#$!% to take the tank out and check it . I don't know when I will get to it . Thanks for your replies . I think I already knew I would have to find a way to get the tank out and check it but was hoping for an easier solution .
Old 05-17-2007, 01:16 PM
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Default RE: Air bubbles in fuel line ?

Here's a little trick... Once you have the tank out, lay a piece of Duct Tape on the bottom, and fold the end of the tape over onto itself to create a tab.

That way if you ever need to take it out again, you have a tab to pull on
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Old 05-17-2007, 06:05 PM
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Default RE: Air bubbles in fuel line ?

Tanks always need periodic repair so you might as well fix them so they can be removed.

Bill
Old 05-17-2007, 06:25 PM
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Default RE: Air bubbles in fuel line ?

I had the same problem once on a Magic with 46 Thunder Tiger. If all the above doesn't work, try this quick check. If it's only at high RPM's, and you have a remote needle valve on back of motor it could be caused by high pitch vibration of the needle valve. The bubbles are vaporized alcohol. On mine I attached the needle valve to firewall, no more bubbles.

Good luck,

Mitch
Old 05-18-2007, 01:55 PM
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Default RE: Air bubbles in fuel line ?

One time I was using a poorly-balanced propellor, and the vibrations
were bad enough that the clunk in my fuel tank was bouncing to the
top of the tank and sucking air instead of fuel. My tank was full of
frothy bubbles.
Old 05-19-2007, 03:04 AM
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Default RE: Air bubbles in fuel line ?

I took the tank out ( was a pain in the butt) and found the the clunk line had a pretty good permanent bend in it . My guess is it was not hanging down in the bottom of the tank at the bootom of the fuel but was curved in such away that it was sucking air part of the time . I will try and run it tomorrow to see if all is well . I replaced all fuel lines to be safe . All your suggestions are good and things to watch out for in the future . This bird was given to me so I don't know if the prop was balanced I will check that too . I added more foam just in case . This is my first Magnum engine I hope it is enough power and runs good . I think it is a .46 which should be enough power I hope . The Sig Somethin Extra ARF seems pretty small and light . I will let you know after my next back yard run if it is running smoother with out hesitation . I called Sig and ordered the wing joiner tube . I am also waiting for my crystal for the RX so I can fly it with my Futaba computerized TX . I want everything right before the maiden and will take my time to make sure everything is right including the wind . Thanks for all your replies .
Old 05-19-2007, 09:51 PM
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BillS
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Default RE: Air bubbles in fuel line ?

Did you fix the tank so it comes out easily?

I have been searching for an air bubble problem for a week and the tank has been out more often than Britney’s panties have been down.

Bill
Old 05-20-2007, 03:00 AM
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Default RE: Air bubbles in fuel line ?


ORIGINAL: BillS

Did you fix the tank so it comes out easily?

I have been searching for an air bubble problem for a week and the tank has been out more often than Britney’s panties have been down.

Bill
[sm=lol.gif] [sm=lol.gif] [sm=lol.gif] [sm=tongue_smile.gif] [sm=wink_smile.gif]

I love your analogy . I took the tank out yesterday replaced all fuel tubing and added foam . I thought the problem would be solved but NOT [:@] . I then decided today to remove the Magnum engine and put on a Os .46 AX engine that I had not run since a pretty good crash last year . The AX has the same problem [:@] . Unless the AX was damaged in the crash it ran real good before but had the same problem as the Magnum . It started with 1 flip even though it had not been run since fall of last year but when throteling up there was bubbles and the engine quite . Actually the tank is harder to get out with more foam . It is back to square 1 with a different engine doing the same thing unless someone can think of what the H is going on .
Old 05-20-2007, 04:13 AM
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Ed Smith
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Default RE: Air bubbles in fuel line ?

I have been searching for an air bubble problem for a week and the tank has been out more often than Britney’s panties have been down.
Did you not know? Britney does not wear panties.

Ed S
Old 05-20-2007, 04:18 AM
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Default RE: Air bubbles in fuel line ?

If you truly want to solve the problem then use a Tettra tank. It has a fuel cell inside the hard outer tank. It solves ALL tank problems.

Ed S
Old 05-21-2007, 04:15 PM
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Default RE: Air bubbles in fuel line ?

Who sells Tettra tanks? I have 2 planes with foamy fuel. I never know how long the engines will run on either plane.
Old 05-21-2007, 05:23 PM
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Ed Smith
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Default RE: Air bubbles in fuel line ?

Who sells Tettra tanks?
Go here.

www.pspec.com

Ed S
Old 05-22-2007, 07:33 PM
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Default RE: Air bubbles in fuel line ?


ORIGINAL: Ed Smith

Did you not know? Britney does not wear panties.

Ed S
What Ed said. He goes in for waxing and gets the Telly Savalis ...............
Old 05-24-2007, 11:31 AM
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Default RE: Air bubbles in fuel line ?

I put the Magnum engine on another plane and it acted the exact same way . I still had the OS .46 AX on the SSE I checked the high end needle valve and I had it open to far . I closed the high end and then opened it 2 1/2 turns and it runs great like it always did . I still see bubbles but the engine runs fine not a single hesitation . I havn't flown the SSE yet because it has been way to windy so I don't know how it runs in the air yet . I am real frustrated with the Magnum engine I have worked and worked at trying to get it to run . It had never been run when he gave it to me . I have no experiance with Magnum engines . Are they all just crap or is there just something wrong with the one I have ? I have 2 OS .46 AX, OS .40 LA , Evolution 46NT and an Irvine .61 all run good so I don't think it is me not knowing how to tune an engine . I am using Cool Power %15 and all my engines seem to like it so I don' think it is the fuel . I put an OS # 8 plug in the Magnum . Any ideas ? Sorry I thought the bubbles were my problem but this thread might have helped someone with all the good enfo on getting rid of bubbles . Not to mention picturing in my mind Britney waxed with out panties [sm=49_49.gif] .
Old 05-24-2007, 12:55 PM
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Default RE: Air bubbles in fuel line ?

I have two questions:

1) Does this engine have a remote needle valve?

2) If it does, are the bubbles between the needle valve and the carb?
Old 05-24-2007, 02:43 PM
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Default RE: Air bubbles in fuel line ?

The needle valve is on the carb . I am thinking the bubbles may have nothing to do with it . It just dose not want to run . I have got it running a few times but it always ends up running ruff or when it sounds good and I think I have it it just stops .
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Old 05-24-2007, 02:48 PM
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Default RE: Air bubbles in fuel line ?

Well, if you're still getting big bubbles, air HAS to be getting in there somehow. If the fuel were foaming, it would still be a bit foamy in the lines, not the giant air-gaps that you described. The only way that can be happening is if the feed line is sucking air. The only way that can happen is if there is a hole in the line, or the clunk is not at the bottom of the tank.
Old 05-24-2007, 03:28 PM
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Default RE: Air bubbles in fuel line ?

This is a different plane I have it on, different tank and different fuel lines . What is the black screw on the top of the carb for ?

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