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Thread: Stuck Carb float?

  1. #1
    Jetfever's Avatar
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    Default Stuck Carb float?

    Approx 800 Hours on Factory reman, and New carb. same total time: LYC O320-B2B, in 1999.

    I was about to fuel my plane when I saw fuel dripping from the Carb air box. Small puddle on ground caught my eye. I shut off the fuel at the cockpit selector, the leak stopped.

    I had just taxied a short distance to the fuel pumps. I called an A&P and he had some suggestions, including tapping on the float bowl with the wooden handle of a hammer.

    This did not fix the problem. I asked if it was OK to taxi the plane back to the hangar, and he said yes, so I did.

    But first, I had a friend stand by with my Hangar fire extinguisher. (Cell phones are so convenient). I waited until all fuel had evaporated. I started the engine with the fuel selector in Off, then turned the selector on after a short period of taxi, and made it to my hangar without a problem.

    The vibration of Taxi back fixed the leak. This has never happened before. I am sure because I would have had the dreaded dark stain on the lower cowling and belly, I had to wipe these (clean but damp) areas down at the pumps.

    I cancelled my planned camping trip to the High Desert over this since I did not want to chance flying, and leak fuel on the trip out, and be at an off airport sight (no fuel available) with a fuel leak, or low fuel state.

    So what should the next step be?

    1. Do you guys always shut off the fuel at the selector when parking? I will from now on. (I have been leaving the selector on left tank).

    2. Do I need a carb rebuild or exchange? There are many opinions around my 'port, from "Don't worry about it, just some dirt", "Add some Marvel Mystery Oil to the fuel", and "Get a new Carb, you only have one".

    Edit: I pulled/ examined the Carb float bowl screen, as well as gascolator screen, no FOD found.
    Last edited by Jetfever; 03-28-2014 at 10:51 AM.

  2. #2
    Gilbert Pierce's Avatar
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    Default Re: Stuck Carb float?

    If your fuel primer is leaking it will drip out of the carb like a stuck float. Block the primer line and see if the drip goes away. Fuel leaks by the primer into the intake port and from there it is down hill to the carb throat.

    This happened to me and I thought the float was leaking. I called Bobby at Aircraft Carburetter in Dallas about fixing it. He said " did you check the primer". Smacked my self on he forehead and headed for the airport.
    When I disconnected the primer outlet line from the primer fuel was leaking out. Cleaned he check ball and no more drip.

  3. #3
    Jetfever's Avatar
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    Default Re: Stuck Carb float?

    Gilbert, Thanks for the quick reply. If this happens again, I will pull the primer line. Problem: The leak stopped after a short Taxi. I don't know how to make the leak start again.
    Try giving the primer a few squirts? I always use the primer when the engine is cold, just to cycle everything on the ship at least once.
    Where is the check ball? Is it in the panel mounted primer? Take this apart and clean and replace O rings?

  4. #4
    Gilbert Pierce's Avatar
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    Default Re: Stuck Carb float?

    There are two check balls. One in the primer inlet and one in the outlet. Two little screws cover them. Remove the screw and you have access to the check ball, seat and a spring. Be careful they don't pop out when you remove the screw. One screw for inlet and one for outlet.

  5. #5
    walt.buskey's Avatar
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    Default Re: Stuck Carb float?

    Steve, I went through this a while back when trying to track down a runs-too-rich situation. Rebuilding the pump is pretty straightforward. As Gilbert said, the two check balls are beneath the screws. About the only other thing is a pair of o-rings, which I replaced. I'll post some pics that may help. Fuel lube during re-assembly is advisable.

    My problem, it turned out, was an improperly-adjusted float level; the tang had been bent so its needle & seat didn't line up correctly, preventing a solid seal. Spacers beneath the seat, to lower it, was what should have been used rather than bending the tang. (A carb shop fixed that.) On the bright side, I now have an operating primer pump, which had been "inop" before.

    As far as shutting the fuel off, I never used to do that on any of my cycles or "yard machines," but after a stuck float and a subsequently drained tank, I always do now. No sense leaving the needle valve/seat to deal with all that hydraulic pressure over extended periods of time. If it leaks, bad for the environment, a potential fire hazard, and --at this point-- expen$ive. Now I make sure I close off all fuel valves when putting machines away.
    Attached Images Attached Images

  6. #6
    flying bee's Avatar
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    Default Re: Stuck Carb float?

    Wow, great pictures
    Craig

  7. #7
    Dwain's Avatar
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    Default Re: Stuck Carb float?

    Yes, thanks for the great pix. - Dwain

  8. #8
    Pacerfgoe's Avatar
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    Default Re: Stuck Carb float?

    Thanks for those pics Walt....sure helps a guy understand whats being talked about.

  9. #9
    walt.buskey's Avatar
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    Default Re: Stuck Carb float?

    Thanks for the compliments! At the middle school where I work, they tell me I'm a "visual learner" and I believe it. I try to document everything I do with pics now, but used to make drawings of everything I took apart.

    btw, in case no one else mentions it, soaking the parts in Hoppe's gun cleaning solvent will really clean them up well, dissolving any old fuel varnish/deposits. The screws, springs and check balls came out spotless.

    I didn't remove my pump from beneath the instrument panel, but did run some solvent through the pump body with Q-tips, then sprayed with carb cleaner to flush it out thoroughly, and finally allowed some fuel from the wing tanks to run through it into a basin for a final flush before reassembly.

    Walt

  10. #10
    Jetfever's Avatar
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    Default Re: Stuck Carb float?

    Thanks so much Walt and Gilbert! Fantastic photos. Great explanation. I wonder if the primer could be my problem, or the float had some dirt, etc.
    I really like seeing the innards of the primer, after using them for over 40 years, and not really giving them much thought
    With this info, I can fix the primer if it's leaking. I don't think I would do the carb other than remove it.

    Great idea using gun cleaner. Here in CA, government, EPA, and other alphabet groups, got involved with Carb cleaner. The stuff available today barely works. When I was a kid, I could clean a M/C or lawn mower carb with a momentary spray, and the carb would go from brown, to looking "brand new" aluminum. Now I can empty the entire contents of a carb cleaner can and the varnish will still be there (brown carb, does not look clean, jets still dirty). Does this help the environment? A whole can sprayed into the environment vs a momentary spritz? Reminds me of the new mandated water saving toilets that must be flushed twice, and light bulbs mandated that are a hazmat if you break, etc. oops, sorry I guess I got political.

    As far as shutting the fuel when parking, I must agree. I had some motorcycles drain a tank (while parked) once or twice in the old days. So why not shut the fuel off after every flight? Might be good to cycle the fuel valve. There is little danger of T/O with the selector in off, the engine will quit B4 you can get to the runway. I'm on a trip, but I'll check my POH when home, "Fuel Off" might be in the normal ops procedure?

    How about Marvel Mystery Oil in fuel?

    Thanks again, Steve

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