fuel tank problems

[Slyfox]

Here's the problem I have. I have one new tank on the left side 13gal tank, put in about 4 years ago. The right tank is an original tank from 1995 time period 13 gal tank.

This is what is happening. I put 5 gal gas in the right tank and it goes dry, meaning the light for low fuel comes on and the header tank starts to go empty, not good. It seems to work if it's full. This gives me the indication that the unusable fuel is 5 gal. If I bank and pull back on the stick, fuel flows again. Not something I like to do. The left tank works all the way down to almost nothing in it, no matter what I do flying wise.

The right tank(troubled tank) has the vent in it at the top for the header. I've tried making the tabs for the cap tighter for a better seal and I have the blue seal from a mercedies fuel cap. I also have the inlet on the cap flared so it catches the airstream, still no good.

This tank picks up from the very back corner. I just sealed that and drilled a new hole twards the bottom center like my new tank, but I haven't had the chance to see if it makes things better. Almost seems like the tank is not pressurizing with the vent in the cap, but I can't see anything wrong with the cap, can blow through it and can seal it up by plugging the inside of the cap.

Any and all thought appreciated.

[Slyfox]

I forgot to mention I pull the strainer and cleaned (it was nice and free) that was on my last attempt. still the same problem.

[Paul Z]

Have you checked the Fuel Line from the Wing tank to the header tank, and checked the fittings?

[SkyPirate]

hmm I could see if your cap vent wasn't "venting" once the header tank level started going down it would null the vent to the tank making the main tank lose pressure to allow fuel to flow back to the header,..basically trapping the fuel in the main with a vacuum,..but you said the cap vent was working properly right?


when you drop that wing your basically burping the sytem from the sounds
Chase

[Slyfox]

replaced all fittings and hoses.

[Slyfox]

cap is venting.

I changed the pickup to where the new tank picks up. Just waiting for weather, stuck with 100' ceilings right now. Oh if I turn both tanks on, the left tank goes into the right, I think that is because the left tank is running full right now.

my testing is being done with the left tank off and the right tank on.

[Slyfox]

one more mention, the left tank(good one) does not have a vent to say from the header, just the right tank has the vent to the header.

[SkyPirate]

on the tanks I'm building I'm installing flop tubes in both tanks,..and I have room to exit thru the bottom of the tank not the end,..



an example
if a tank is say 24 inches wide by 48 inches long that's 4.987 gallons in the tank if the fuel level is 1 inch up from the bottom...so if the outlet of the tank is also at 1 inch up from the bottom ..it will leave approximately 5 gallons in the tank,..providing tank is flat and level etc

anyways ..when you get a chance to fly ,.let us know the outcome of your modification

Chase

[SkyPirate]

"one more mention, the left tank(good one) does not have a vent to say from the header, just the right tank has the vent to the header."

if both wing cap vents are working properly ,..it should not matter if there is only one vent from the header to one tank,..not both ,..it almost sounds like a vacuum is being established somewhere that it over taking the vent in the right tank ..since the vent goes from the header to the right then to the left thru the transfer line,..is there a check valve anywhere in the system?

Chase

[Slyfox]

No check valves. Just individual on/off valves each tank. The good tank left has no vent line to the header.

I to thought of a flop tube. My question, why does the new tank work so good. I can do 90degree banks to the left with that tank and I never get a low fuel warn which works off the vent line off the header tank, I run this tank down below 5 gallons all the time. Right tank, a real sorry thing. No such luck.

I even thought of putting a 90 tee and run the fuel line off the fuel check valve on the bottom of the tank.

[Dave S]

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

[Slyfox]

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.

[Dave S]

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

[Dorsal]

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)

[akarmy]

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.

[Slyfox]

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.

[Slyfox]

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.

[cap01]

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

[Slyfox]

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.