While I understand how to route the tubing, I don't understand what keeps the fuel from just running through the engine while it's being filled. Please fill me in

Thanks

Kerry

Well here is my setup: Fuel pickup line(to carb) has a T on its way to the carb and a small (2 inches) piece of tubing on the leg of the T so to speak and a clamp to close it for normal engine runing. I use this one for emptying the tank since it goes to the clunk. And the third line I run out of the cowling and this one I use to fill up till fuel comes out of the muffler and close it with a self tapping screw. Hope this helps

The only thing that keeps the fuel from running through the engine while the tank is being filled is the throttle being closed.

Andy

Andy is right...with the throttle closed and the "pressure" line open, the fuel will follow the path of least resistance for overflow - the pressure line.

Actually, what does it is that pressure takes the path of least resistance.

If you fill your tank from a third line, the pressure in the tank has two ways to escape. It can push air out of the vent hole, or push fuel through the same size hole. It's much easier to push air through so that's where it escapes.

Now you MAY push some fuel into the line, but even if you do, it will be a slow trip all the way to the carb. And if, by chance the fuel makes it all the way to the needle valve, it will create even MORE resistance.

So you MIGHT get a little fuel in the carb, but certainly not enough to worry about.

And if you ARE getting a lot of fuel in tha carb, you need to examine your fuel system... There's a problem somewhere.

I use a 3 line system on my Sukhoi and I don't even bother closing the carb fully before fueling. I just add fuel and the excess comes out of the muffler. I've never had a problem with fuel flooding the carb.

Got it. Thanks for the info.

Kerry

I prefer three line systems whenever it is possible to install them. Can't be done in some aircraft. Most builders use muffler taps to pressurize the tank. If that line is in the open where you can reach it just disconnect it from the muffler. Being in the highest part of the tank it will vent so no fuel reaches the carburetor. When the fuel starts to come out the pressure line your tank is full.