When a fuel tank is 1/4 full and the nose is down, how does the clunk get to the fuel if it is in the abnk of the tank? My engine always stalls when the nose is down b ecause fuel will not go into the engine?

I've heard alot about issues with fuel tanks and to be honest i don't know the answer. But mabye someone else does and will read this.

Presuming the tank is correctly set up, the clunk (the metal fitting on the end of the fuel supply line) will drop to the front/bottom of the tank, and remain in the fuel.

Essentially, again if the tank is set up correctly, the clunk is "free"...that is to say, it can rattle around anywhere in the tank it needs to. As a result, no matter how the tank is tipped, the clunk falls to the lowest point...exactly where the fuel is.

One of the common problems with tank setup is cutting the supply line too long. As a result, the clunk either gets wedged against the back of the tank, or the line is too long to allow the clunk to "bend" it, and fall to the front. This sounds like a likely suspect for the issue you describe.

When setting up a tank, cut the line so that, if held "upright"...that is, with the plug at the top...the clunk will dangle about half an inch off the "bottom" (the back if the tank is mounted flat) of the tank.

Here in a moment, i'll make up a couple drawings to indicate what I mean.

Here's what I'm talking about...sorry about the quick and dirty drawing.

so the clunk should be able to do a 180 and move to the front?! My clunk will ony stay in the back of the tank.

well don't forget there is pressure in the tank and centrifiugal force... my cluck is off the "back of the tank" but the line is too thick to allow the cluck to fall forward. I don't have a problem with flameouts either..I guess cause you don't have full power on when you're vertical down for long. if you're engine is dying when your vertical down then you have a prob with the lines or with the mixture.

well its not even a vertical problem, its when I come in for a landing. When the engine is slightly down for the approach, it dead sticks. Air gets in the line and shuts off the motor. I am using a pitts muffler. Maybe a backpressure prob?

No the clunk should not be able to go to the front of the tank. If the clunk line bends and sticks in the front it will give you more problems. Went I set my tanks up I put a piece of brass line inside the clunk line so it can't bend forward ever.

I'd check to see if it isn't stuck forward all ready. Can you even see your tank?

I think you have some other problem besides the cluck, even if you only had small amount of fuel in the tank and you nosed down there's still fuel in the line, you couldn't nose down long enough to run out. If your getting air bubbles in your line its probably because theres a small pin hole in a line or the tank itself or a problem with the stopper cap.

What kind of plane is it?
How is the tank mounted?
Is it high or low in relation to the needle vavle?

-Steve

Hey sthone--how far do you run that brass line in the fuel pick-up line?

You don't need much, just enough to make the line too stiff to fall to the front of the tank.

Ken

Who says a picture is worth a thousand words. Amen. Thanks

its a .40 great planes cub. The tank is actually about 2 inches below the need valve which may be a problem, however, the plane is designed like that or the cowl wont fit. It's not an air leak because I bought al new lines and replaced the tank twice. The pitts muffler has 2 gaping holes, maybe its a pressue problem? Whenever I point the nose down, the engine runs for about a minute then dies. Maybe this is normal?

did you change the lines inside the tank that go to the clunk?

I think your problem is the tank being too low and creating a fuel draw problem.It is just coincedence the engine dies when the nose is pointed down.at full power you are getting muffler pressure plus a full tank (head pressure)to help feed fuel to the engine at idle the pressure in the tank will slowly bleed of to 0 and a tank with low fuel has less head pressure to feed the engine.I have built 3 cubs and there has always been alot of room behind the firewall what is preventing you from raising the tank up?formers can be cut away to allow the tank to be raised

Can you reproduce these results on the ground?
Hold the plane tip the nose down with the same amount of fuel your flying with.

-Steve

Exactly which Cub do you have?

Hogflyer

I want to know how high you're flying if you can fly nose-down for a minute without hitting the ground.

When you say a minute do you mean simply momentarily or actually a minute? I am by no means an expert but have had simular problems.As stated above you dont want the clunk to fall forward because it will pinch the line and you will starve it anyway.When in a dive you will not be applying power(I hope) therefore the engine will continue to run even though the clunk may not be covered with fuel.If you are acually talking about a minute or close to it nose down under power it will starve itself in my experiece.

Image test. Please ignore

on the ground it will stay running for 30 secs. My avg approach lasts 45 secs or so and the engine is stalled by the time it hits the ground. Yes, the formers are preventing me from raising the tank. Should I cut away the top former and raise the tank? How should I go about it? Please hep get this thing flying!!!.

Didn't you say that this was the Great Planes Cub??? If so, I've got that same plane. I installed the tank in the stock postion and haven't had a bit of problems with it. And yes, I've used a Pitts muffler on it. I really think that the problem would lie with something other than the tank position.

Ken

I have a Dura Plane (brick) that has the same problem.I removed the tank and replaced the clunk line(looks just like the drawing earlier in this post) but when the plane is nose dow,it sucks air and makes the plane die.I can see it when I hold the plane,and tip the front end down,it idles right down and will stall unless I tip it back level or upright in the front. I am so used to dead stick landings its not funny,maybe 1 out of 12 time I can keep it running. What about a small header tank? I also have a Hanger 9 tribute I am leary of flying because I'm afraid it will dead stick and not being used to it might crash.I am running a 40LA engine.I know what you are going through!!!!!

It is possible that the clunk HAS moved to the front of the tank. this can happen in a hard landing or nose over . grasp your plane FIRMLY by the landing gear and snap it backward sharply now gently shake it to see if you can hear the clunck bouncing in the tank. you should be able to hear it move. I under stand this can happen to any one but it NEVER happens to me...LOL

Raising the tank won't help.

You said, "Whenever I point the nose down, the engine runs for about a minute then dies."

Does it do this on the ground with a full tank? If it does, my guess is that you are rich on the low end. The added pressure of the fuel (when pointing the nose) down is flooding it.

If you think its the tank hieght try turning the plane up side down and see if it still dies. Upside down the tank would then be higher now.....Just a thought.

Does this only happen at say idle when your coming it for landing to would it happen also if you were to say dive at half or full throttle?

I still think you have some other problem.

-Steve