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.