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Thread: fuel tank problems

  1. #11
    Senior Member Dave S's Avatar
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    Default Re: fuel tank problems

    Hi Steve,

    Won't be so bold to say I know the answer; but - it sounds like the right tank fuel line may have some intermittent restriction.

    FYI - sitting level, our 13 gallon fuel tanks came up to about a pint unusable on each side.

    A couple questions

    1) Do you have anything, like a filter, or strainer, in either line going from the wing tanks to the header tanks? If you do - I'll confess my experience with this issue....

    2) What design valves do you have in the tank lines? Are they a smaller ID than the lines?

    3) Is there any possibility of a flap of material or something else floating around in the header vent line or the right wing tank line; or, any possibility that the fuel line has swelled partially shut on the inside where you cannot see it?

    4) Do the fuel lines and header tank lines avoid any loops?

    Sincerely,

    Dave s

  2. #12
    Senior Member Slyfox's Avatar
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    Default Re: fuel tank problems

    I have bing fuel hose straight from the tank to the valve which is a ball valve, been using them for years and has the same setup for the other tank. I did make it out to fly and found that it quits flowing when it wants to, start with a few bubbles and than stops. I did put an inline filter on the line this time, mainly to watch flow. Very interesting, when it stops there is fuel at the tank down about 1 inch in the line leaving the tank, than about 8 inches of air, than the filter is full of fuel. I bank to the left and put in right rudder, knife edge or you can call it a slip possision, than I have to wag the tail with the elevator. Than the fuel will start flowing again. Like its vapor locked. I did a bunch of pattern runs and hit and miss weather it's going to stop flowing on the down wind after a hard right turn. One time it quit flowing, next time maybe not. All the way down to the runway no flow, lift off and bank the wing and rudder thing and than elevator wag and the flow comes back nice and strong. Next time I just take off and the flow is nice and strong. this is with 5 gals in the tank.

    maybe I need a facit pump on that tank to keep things flowing, don't know at this point. I think if I fill the tank all the way it will work fine. Just trying to increase usable fuel in that tank.

    I did look at the newer tank and it has a depression on the bottom that leads to the fuel line and strainer. Must have been a big problem with the older tank that they changed it.

    Putting a flop tube might also be an answer and build one like in an RC airplane, hose off the inlet and a weight at the end with an opening to keep it in the fuel. I think the opening is 1/2 pipe will need something with 1/8 pipe opening on both ends for hoses.
    steve
    slyfox
    model IV 1200-flying
    912uls
    IVO medium in-flight
    RV7A-flying
    IO-360
    constant speed prop

  3. #13
    Senior Member Dave S's Avatar
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    Default Re: fuel tank problems

    Steve,

    With the ball valves you have - they should not be a problem since the open position is basically the same as having unobstructed tubing anyway.

    Our fuel tanks, being the newer design, have the depression at the fuel discharge point from the rear of the tank.

    I had an experience, similar but not identical, to your experience when I put filters on the lines between the main tanks and header tanks - they would simulate a vapor lock if any air hit the filter - the flow would start again if I pressurized the main tank a bit until the next bubble hit the filter. Starting with a dry filter allowed the fuel to flow freely; but, once the filter element got wet with fuel if any air came in contact with the filter afterward it would it would do the simulated vapor lock thing. Interestingly - a full fuel tank would not permit the problem to develop, but a partial fuel tank would.

    Getting rid of the filters in the lines from the main tanks put an end to the problem - hasn't occurred since. I won't put them back in - ever.

    FYI - I do have a Facet fuel pump installed at the low point between the console fuel valve and the firewall - mainly to pressurize the fuel system for a quick start but also for a backup to the engine mechanical pump. I do not run with the fuel pump on - only for pre-start. The other deal with the Facet, if I understand its performance correctly, is that it "pushes" but does not "pull" worth a darn. Flow testing the system with the Facet in place did not show the flow was restricted because of the pump (with the pump off).

    One of the other folks on the list indicated a potential problem may occur somewhere in the line between the main tank and the header tank - I think that is a likely place to start.

    A person could experiment with disconnecting the line and/or the vent line going back to the tank to see if that affects what you are experiencing.

    Anyway - a few ideas - when you find out what the cause is - it would be interesting to know in case the rest of us get a similar situation sometime.

    Sincerely,

    Dave S

  4. #14
    Senior Member Dorsal's Avatar
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    Default Re: fuel tank problems

    Dave,
    Not sure if i should put this on a new thread but I am curious as to why the Facet would help with starting? Given the wing tanks there should always be about 1 psi at the carbs which should keep the bowls full, in fact it is my understanding that in the case of a fuel pump failure the engine will still run on head pressure alone (though not at full power). Do you notice a big difference starting with and without the facet? (BTW which Facet are you using)
    Dorsal ~~^~~
    Series 7 - Tri-Gear
    912 ULS Warp Drive

  5. #15
    Senior Member akarmy's Avatar
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    Default Re: fuel tank problems

    I just removed my facet pump from my system and yes with a fresh new dry fuel system, I put in 5 gallons of fuel and it primed and started just fine. Maybe a few extra blades pulled through. After that it starts first blade every time. I also tested it by pulling the fittings and yes it flows from the wing tanks under gravity alone.
    Andy Karmy
    Kitfox 7 - 912S - SOLD
    Auburn, WA

    http://kitfoxflying.com

  6. #16
    Senior Member Slyfox's Avatar
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    Default Re: fuel tank problems

    I may find that my problem is basically the tank. May have to replace the tank and put in a new one. Like I said the other tank works perfect.

  7. #17
    Senior Member Slyfox's Avatar
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    Default Re: fuel tank problems

    finally fixed this bugger. What did I do? Well I changed the tank. I put 5 gals in it last night and did some fun t & g's, yup, got a little surprise after take off, the winds went from 050 &4 to 310 @ 17 gust to 22. I took the sod and did a few in these winds. Oh and the runway is 3/21. Lots of fun. Got to love these kitfox's. Anyway an hour flight and only at the end of the fuel did it have a little problem with a hard right turn, right tank. I now have good usuable fuel. The new tanks are sure nice and there was nothing left over inside from the construction, thanks John.

  8. #18
    Senior Member cap01's Avatar
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    Default Re: fuel tank problems

    steve . what did you come up with for a max quanity in the new tank ? i installed a new tank last winter and was able to measure in 14 gal
    chuck
    kitfox IV 1050
    912ul warpdrive
    flying B , yelm, wa

  9. #19
    Senior Member Slyfox's Avatar
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    Default Re: fuel tank problems

    14 is about right with the left tank which is a newer tank. This one is still in the works for how much. You see I check for usable fuel in flight. Meaning when the red light comes on, on the panel, than it's empty or the rest in the tank is unusable. Than I go and fill that tank on the ground until full and take my usuable fuel from that. It hasn't quit happened yet, next flight should determine that.

    I have a low fuel warning on the vent system of the header tank, as soon as the fuel quits the light will come on. so testing the tank in the air works very well. I wouldn't trust running the tank empty on the ground by no means.
    Last edited by Slyfox; 05-12-2010 at 02:55 PM.
    steve
    slyfox
    model IV 1200-flying
    912uls
    IVO medium in-flight
    RV7A-flying
    IO-360
    constant speed prop

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