Hello, I am not new to rc but am new to closed cowl airplanes. I have a tf p-40 with a great planes filler valve. How do you know if the fuel tank is full? On my "open engine" planes I used to just crank fuel into it untill fuel would come out of the muffler line. I just thought of this little problem. thanks, hope to maiden it this weekend.[&:]

traxxboy, just fill like you used to, fuel will still come out the muffler line, all the fill valve does is by-pass the the needle valve. Hope this helps.

wow thanks for thee quick response, and yes it does help.

traxxboy...those filler valves are prone to leaking air..If your engine starts acting up, bypass the filler valve and see if it cures your problem..and replace with a fuel dot and an independent 3rd line.
Don't worry you'll be ok for awhile just trying to save you problems down the road..

Fill valves really have lousy track records. I don't know anybody who has used one that hasn't gone to other methods.

What any of the methods boil down to is having two holes in the cowl versus one. And then, what you make those holes look like.

There are somewhat expensive plugs that look pretty nice. Fuel dots, I think they're most often called.

And there are cheaper ways.

In those pictures, the forward line is the fill line. The rear is the overflow. That airplane happens to have a uniflow setup in the tank. So it was a 3 line tank to start. So the overflow line is simply a straight line back to the tank pipe that is the overflow pipe inside the tank. The fill line you see goes to a T in either of the other two lines. I'm not even sure if it's the pickup line or the pressure line.

To fill, I pull both lines out like in picture 3, pull the two plugs and fill through the front line. When the back one spits, I plug the two and push them back like in picture 4.

The plugs cost something like 50cents each. I'd make my own, but why?

I am going to try the filler valve since its already installed....however I know whats coming off first if the engine does start acting up. Thank you

I too have questions about this. Working on a showtime with my first four stroke engine(Saito 91). Engine will be covered by the cowl. I have a T-fitting to place in line with the Needle valve to fill....but what about the overflow? Do I also "T" the muffler pressure line? The engine will be almost inverted....Head will face 7/8 o'clock postion. Can I just watch for overflow from muffler? Or will this cause issues starting? Would I be better off using a 3 line system for filling?

The needle valve line is usually the choice because the needle valve acts as a partial plug. However, four cycles often have bent tubes from the head to the carb, and those can catch every bit of fuel that fueling pressure pushes past the needle valve while pumping the tank full. It usually doesn't happen when the 4C is on it's side or rightside up. The tube is updraft and points down when right side up..... yeah..... so won't fill up except when pointing up. OR SOMETHING LIKE THAT!! [sm=wink_smile.gif] Anyway, your fueling technique can uncover the problem. If you wind up flooding the engine right off the bat, be prepared to either fuel differently or setup the plumbing differently or get yourself a hemostat.

Best case is where the overflow line is reachable. And can be disconnected. But the overflow line has to do one thing for sure. It's got to be connected to the tank pipe that goes into the tank to the top, where the "over" is in the word "overflow".

Overflow in the muffler works if the overflow can hit the ground without having to fill up the muffler or such. If the pressure fitting doesn't have an almost straight shot at the ground, it's probably best to do the deed some other way.


T fittings in the pressure line, when it goes to the top of the tank usually work good as an overflow. You may waste a bit of fuel, but it beats how much you waste watching for fuel to pour out of the muffler.

T fittings in the delivery line usually work ok for filling. Needless to say, if you were to run a filler line into the tank that is capped when not filling, it'll solve any problems that happen with filling the tank through a T off another line. That dedicated line will need to go to a pipe in the tank that goes to the bottom of the tank for it to work to empty the tank at the end of the day. But beyond that, it's almost foolproof.