The Stovebolt Site Forums The Shop Area Engine Shop Strange Fuel Filter Behavior

Hello, Folks!

I have got strange behavior on my '46.

She has a 216 and I've got one of those Sediment Bowl filters in line before the Carter W1 (the filter housing takes the AC GF124 paper filter, but there's a FRAM equivalent in there now). This really hasn't ever been a problem except when I let it sit longer than a week or 2.

Unfortunately, Life happened (got married, had a kid 9 months later), and the truck has been sitting for a year or two.

I've been trying to get the old girl started again. The gas got too skunky to use while she was "resting". I drained out the tank, and replaced the fuel.

I'm noticing that where before, I would be able to fill up the filter bowl and have the fuel stay in there, it's now disappearing very quickly once the starter stops cranking. All of the fuel that was above the bottom of the element seems to disappear right before my very eyes.

I know it's not coming out the "Out" side of the filter, because I took the line off of the carb and watched it.

I'm thinking that there may be something going on the Fuel pump -- maybe a stuck check valve? The pump is the stock pump and was rebuilt about 5 or 6 years ago.

Does anyone have any ideas?

did you pop the top off the carb and make sure the needle and seat valve is not stuck closed? You could have a couple of issues. If, when the carb was full adn float up at the top, the needle stuck closed, your carb could be dry now and not allowing any gas in. That would create pressure between the pump and carb. Then, if there is any junk that got in the pump, and is holding a check valve open, it would either not create the proper pressure, and/or drain back into the tank. I would at a minimum take the inlet line off the carb and make sure you can blow into the carb to ensure the needle is not stuck closed. Then, put a piece of fuel line on the line soming out of the pump and make turn engine over a bit and make sure fuel is coming out.

There is a small (3/16 inch maybe?) brass tube in the air intake coming up to the top at about a 45 degree angle. It is called a bowl vent.

Acquire a squeeze bottle (an empty mustard or ketchup squeeze bottle that has been thoroughly cleaned will suffice), fill the body with fresh fuel, and fill the carburetor bowl through the bowl vent.

Let set for several hours!

One of the "benefits" of our modern fuel is that when allowed to evaporate, it leaves a sticky, gooey film over everything; so as mentioned by 69cuda, the float and float valve may be stuck. GENERALLY, the fresh fuel will disolve most of the crud.

Jon.

Those are good tips on the carb end. Thanks, I'll check those out.

Unfortunately, I've ruled out the Carb as the source of the problem because the gas in the filter bowl still disappears when the fuel line between the outlet on the filter and the inlet on the carb is disconnected. (It does it with the filter connected to the carburetor as well)

It almost looks like it's backflowing out the inlet on the filter and back into the fuel pump on the side of the block.

my dad has the same issue on his 40 chevy sedan, he put an electric fuel pump inline with a toggle switch. He turns it on for a couple minutes before he fires it up... problem solved. Pretty sure it is not supposed to do that though!

Agreed!

I'll take the line off of the outlet on the fuel pump and see if I get drainage.

Brendan M has the best check. There is some check valves in the fuel pump. If crud or wear has made them leak, then gravity will do it's thing and fuel will drain back to the lowest point. More noticeable with a low or almost empty tank. A filter between the tank and pump can help if it is dirt/crud. A rebuilt or new pump may be needed if the issue is wear. Some fuel lines are too close to hot spots on the engine(routing matters). Fuel in the line heats up and vaporizes. Pressure will then push that fuel back past the check valve in the pump. The results are the same. Removing the line from the tank to the pump with a cold engine will check the check valves. Do the same with a fully warmed up engine will check the "vapor" pressure issue. Be safe please. Block the line from the tank(gravity still works). No fires please.

Oh, the petcock on the tank will be shut prior to unhooking anything.

I have a similar setup. As stated there are 2 check valves in the fuel pump, one to keep fuel from back flowing from the carb to pump and the other to keep fuel from back flowing from pump to tank. They also work together to pump fuel under pressure to the carb but that's another story.

Another quick check you NEED to do is to check your engine oil level to make sure it hasn't risen or have a gas smell to it.
If the internal pump diaphragm leaks, gas can make it's way into the crankcase.
Hopefully that's not the case and the fuel is just back flowing between the tank and pump.

Good luck
Dave