Carburetor Help

I rebuilt 2 Marvel Schebler TSX carburetors both leaked out the air intake. They had nos needle and seat and USA made floats. Floats were set 1/4 in. Is there any other reason that would cause this problem. I did the tap tap on the bowl and opened the drain to clear needle and seat.The inside is spotless and both carburetors run excellent but after shut down they slowly leak fuel into the air intake. What am I missing.

The gasket under the seat is hard material , so you really have to crank down on the seat. Grind off an old chisel or tool to be sure good fit in slot of seat.

You are missing the act of shutting off the fuel at the tank. The seats can leak where screwed in, and the seats/needles will seat themselves over time, but always shut off the fuel. Shutting it off then letting it run out of fuel to stop. Then shut off the ignition. Jim

I have done a few of these over the years and made that tool out of a wood bit with a T-handle
but I will take your advice.

" Shutting it off then letting it run out of fuel to stop. Then shut off the ignition. Jim" I have practiced this procedure forever & it has always been good for me.

A couple things need to be checked.

Clean fuel and tank are essential. There should be a screen in the inlet fitting of the carb, a screen on top of the sediment bowl, and a screen inside the tank. Sometimes the one inside the tank rusts away, and if there is rust or debris in the tank it will find it's way to the needle and seat. Only takes a microscopic speck to keep the valve from sealing shut.

One thing I like to do is open the fuel valve and let the line flush before making the connection to the carb fitting, especially if the area is dirty and difficult to reach.

Inline filters are sometimes too restrictive and a source of leaks. If you do use an inline, use a screen type made for gravity flow. Paper is too restrictive.

If flushing the valve by draining the bowl doesn't fix it, take the bowl back off, double check the seat is tight down on the gasket, and the needle/seat is clean. Be sure the float is free and not touching the sides of the bowl.

And before putting the carb back on, turn it upside down, suck on the fuel fitting, put your tongue over the hole. It should hold vacuum. If it won't something is wrong and it will still flood.

Hey ww2n -- some times I find the float has been pinched a bit and it wont float good enough -- also it can be a bit brown or green making it heavy when wet-- I have drilled a tiny hole in the float and give it a shot of air to bring it out to full size then solder the hole shut-- the next thing to do is polish the float and get the corrosion off -- the better it floats the better it will shut off the fuel flow! Good luck !! Roy

Thanks all.

I agree with others, on a good running carb, shut it off at the tank and don't worry about it. On my 6 good running antique gas tractors, I can't tell you if the float valve will hold gas overnight in any of them and have no plans on finding out.