Fuel Problem

I have an old '76 Chevy c60 with a 350 engine. After a few days carb. bowl is emptied because the fuel drains back to the tank making for a lot of starter grinding while the fuel pump refills the bowl. What is causing this and what to do about it. Thanks for help.

(quoted from post at 07:49:45 09/21/11) I have an old '76 Chevy c60 with a 350 engine. After a few days carb. bowl is emptied because the fuel drains back to the tank making for a lot of starter grinding while the fuel pump refills the bowl. What is causing this and what to do about it. Thanks for help.

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Depends on what carburetor is on it, but it is either a defective diaphragm in the accelerator pump, or a cracked fuel bowl. Both issues allow the gas to drip through and enter the intake manifold and then into the engine. The gas is NOT leaking back into the tank. You're going to have to pull the carb off and give it a look see.

Does it have a quadrajet (4V) carburetor?

If so, this is a common issue that can be cured by PROPERLY rebuilding the carburetor.

The fuel does not drain back to the tank but, rather, into the intake manifold.

Dean

A 350 in a C-60 would probably have a 2 barrel 2GC (or some version of)Rochester on it, a 366 would have a Holley 4-V with a vacuum governor, I would try a new fuel pump first.

OK a mechanical fuel pump has a diaphragm in it to both create vacuum (suction) and pressure. It also has 2 check valves. When on the suction stroke it pulls the pressure or out side valve closed and sucks the intake side open pulling gas into the chamber. On the pressure stroke it sucks the intake side closed and when it builds enough pressure pushes the out put side open sending gas to the carb. If one or both of the valves is bad it may still work but not well and can take a little time to prime itself. It can also allow gas to drain back into the tank from the lines and pump. It will not siphon gas out of the carb becasue of the design of the carb. Gas enters the carb through the needle and seat that is controlled by the float. Every carb I've worked on has the needle and seat in the top cover and there is no direct line or tube into the gas in the bowl from the fuel line.

So take the air cleaner off and with the choke plate open manually operate the throttle lever while looking down the throat. You should see gas squirting into the throat on a car of truck engine. If not the bowl may be empty showing a fuel supply issue or the accelator pump in the carb is bad. If it kinda just dribbles the accelerator pump is bad or they is a plugged passage in the carb. If as you say the bowl is empty then you have a carb issue that will require rebuilding or replacement. You can check that by disconnecting the fuel line at the carb. If it starts to dribble and or squirts gas as you are taking it off stop. You can test the fuel pump by taking that fuel line at the carb and installing a fuel presure gauge (smart safe way) or just leave it off and bump the starter. If you get pressure or gas pulses while cranking right away you have eliminated the fuel pump.

Sorry it's long winded.

Rick

if you want to try a "down and dirty" napa used to sell a replacement fuel filter that had a check valve in it to stop fuel drain back. i called our local napa up here just for grins and giggles, and they are still available. you may want to toss one of those in there and see if it cures the problem. a lot cheaper than throwing a pump or carb rebuild in 'er. the filter replaces the factory type in the carburetor.

It's not possible for the fuel to "drain back" from the bowl since the float valve is not on the bottom of the fuel bowl. If anything drains back, it's from the pump only. If it has a Holley carb, it's possible the power valve vacuum diaphragm has a hole. All it takes to pop the diaphragm is one good sneeze back through the intake. Usually they run very rich when that happens.
Most likely what's going on is the fuel is boiling out of the carb. Make sure the gasket between the base of the carb is the thick insulator type and not just a flat piece of gasket paper.

Take off top of air cleaner. Look see if choke is properly closed. Usually have to pump accelerator one time to close choke. Dave

I had that problem with my truck. The quickest fix is an electric fuel pump. Turn the key on for a second before you try starting and it will fill the carb. Mine was on a 261 6 cyl. with same problem.