The Stovebolt Site Forums The Shop Area Engine Shop 53 Chevy with 250 IL 6 & 2 barrel carb

This same issue happened before I put the new motor in. Same carburetor. Mechanical fuel pump with an electric backup.
It seems to happen after driving 25 minutes or so, then stop for several minutes (with motor off or left on). I begin driving again and within minutes it acts like it’s running out of gas. If still moving good I can flip the electric pump on and it seems to catch up and do fine , even after turning the electric pump off.
The last time it stopped I was at a stop sign & I pulled off the road & started checking things. The fuel filter had very little gas in it. Gas pours out of the gas line if I remove it from the tank.
I had the electric fuel pump running (it’s between the carburetor & the mechanical fuel pump. No gas was coming out. If I suck in the line while the pump is running I can get enough gas in my mouth to spit out.
A young man stopped to lend assistance. We figured the out line from the mechanical pump was getting air at the pump. The 99 degree elbow was loose. It’s just in a bad position to have it tight.
I turned it tight as it would turn with the electric fuel pump on & turned the motor over. It began pumping gas.
So I reason that it is losing prime due to a leak at that elbow. I can’t tighten it any more. So I put permatex gasket maker over the threads. I drove it last week & it did the same thing. I got home by turning in the fuel pump again until it started running again.
Can someone have other ideas for me ?

If it was leaking there, it might be leaking elsewhere. I would recommend checking all of the fuel line fittings in the system.

That said, if it still leaking, then it is either not tight enough or the fitting is damaged.

Pulling it apart and carefully inspecting both sides would be another good choice.

Permatex gasket maker is silicone based and does not hold up to gas. Find another sealant that is meant for gas.

I recently had mysterious conkouts with my Coupe DeVille. Went though the basics and came up with nothing. Fuel filter wasn't clogged but it looked like I wasn't getting fuel to the carb even with a fully rebuilt and tested fuel pump.

Car started and ran great but could conk out after 20 minutes, 20 miles, who knows> Sometimes I could get it started sometimes not.

Anyway, the only thing I could come up with that was causing the problem was a blockage somewhere between the tank and the pump. I replaced the tank and the entire steel fuel line from the tank to the fuel pump - about 20 feet of steel line.

Haven't had any problems or hint of problems in the 500 miles I've driven it since the repair.

I found no smoking gun but the tank and line were original 68 year old items. Rust? Piece of gunk wedged somewhere in the 20" pickup tube inside the tank? Something in the 20 feet of line? Who knows? Don't take anything for granted even if it "looks clean" or you can blow air through the lines.

There was no visible rust in my tank but something wasn't right.

Oh ya, Friends kept telling me it was vapor lock and that I needed to install an electric pump. Everybody seems to think every mystery problem with a car is vapor lock. It never is.

Thanks everybody! I thought about vapor lock but ruled that out.

The next time you turn off a hot engine, and allow it to be at rest for several minutes (hot soak):

Start the engine.
Run the engine at a fast idle (1500~1600 RPM) for maybe 30 seconds before starting to drive.

Costs nothing to try.

Jon

Well . . just for "giggles" - your Electric fuel pump is "between the mechanical pump and your carb" ?

The electric fuel pump - - should be , back close to u'r fuel tank ; and , thus pump forward , towards the engine. Some of those elec. fuel pumps , don't work very well = having too "suck gas" that far.
I had this very same 'problem - on a 79 Ford truck' ; that I fought for over a year. I'd pull over and remove the TOP of the 2bbl carb . . . . the float chamber, would be 'dry' .
I was using those "small clear fuel filters" , too see if my fuel line was running dry . I fought this "condition" for a long time (even replacing that carb with a brand New 2bbl stock carb) .

Turns out - - - I would keep changing out - - - those clear fuel filters ; but never checked the "stock fuel filter" (that filter , that "screws-into the carb float chamber" ).

See , what I'm saying - - - I would change ONE fuel filter & not even check any other "Fuel Filters" ............................... that stock , screw-in Motorcraft fuel filter , was my "problem" .
So, make sure too "not focus" , on just one issue (meaning = Check all your fuel filters ) . What carb are you using on your 250 engine ? ?

jim

Permatex did not work, the threads are not tight on the exit side of the mechanical pump. I may have to remove the mechanical fuel pump to tighten the out side side of the line.

I don’t believe this carburetor has a separate filter. The valve cover does have baffles that the PCV go in between.
The gas line does not leak gas at the pump, it allows air to escape (not making a seal) if that makes sense?

How many filters do you have? Everywhere you have rubber hoses and clamps is a potential source of leaks and air introduction to the system.

Simplify your fuel delivery system and get rid of all but one filter. Try to use steel connections wherever possible instead of rubber hoses clamped to metal tubes.

As stated above, I had similar issues with an old tank and a fuel line that had several "repairs" in it (damaged sections cut out and replaced with rubber hose or a filter).

Anyway, the carburetor will normally have a little screen in the inlet port or a screw in metal filter where the pump to carb line comes in.