The Stovebolt Site Forums The Shop Area Engine Shop Very hard to start

Hi Guys, My '52 GMC is a bi**h to get started. First the background. It has a 1976 Nova 6 cylinder in it. when I bought it the guy said it had been garaged for almost 10 years, and all it needed was a fuel filter. YEAH. Anyhow I bought it cheap ,replaced: fuel filter, plugs, wires, had the gas tank cleaned and coated while installing a new fuel sending unit. The problem is you have to pump the gas 30 times to get it going. After that it runs fine. Fast idle works, choke appears to be working. Only thing ...the glass fuel filter is never full of gas whether running or not. Fuel pump maybe? Thanks and Happy Belated Turkey day.

Could be the plunger in the carb that sends that extra shot of fuel when you pump the gas pedal. (The accelerator pump)

Hey Terry,what type of fuel filter does it have? Just wondering if the filter is installed with the direction of the fuel flow. Could also be a fuel pump. Notice any leaks anywhere after the truck sits for a while?

No leaks. I installed the seethru filter .. Maybe I put it on backwards? I thought fuel pumps either worked or not?? Terry

checked the fuel filter , its on right. Turned the motor over with it off and she spurted gas....not steady, but like your wedding night. wadda think......carb?

Terry - the next time you go to start it cold, try NOT pumping the footfeed. Crank the engine for about 6 seconds, then pump the foodfeed 3 times, depress the footfeed to the floor, and then take your foot off. Now see if the engine will start (NO FOOT).

Jon.

ok keep you posted.....Thanks

Item 1: Fuel pumps can deteriorate over time and adversly affect their pumping ability. They contain a diaphram, spring, check valves, and a mechanical lever. Failure or weakening of any of these components can cause inadequate fuel pressure, fuel flow, or their ability to hold a "prime" (fuel within after the engine is shut down). Fuel pumps are tested using a fuel pump volume and pressure tester to measure both pressure AND volume. Low pressure usually means a weakend spring or diaphram. Low volume is usually a bad inlet or outlet check valve. Either way it means rebuild or replace.
Item 2: The carburator, way too often the carb gets blamed yet innocent. During normal cold starts there are several circuits within the assembly that provide fuel to the bore of the carb. The float circuit, the idle circuit/low speed circuit and the choke circuit.
When starting a single depression of the throttle pedal should close the choke valve,(auto choke)closing of the choke valve allows both the idle and low speed jets to meter fuel to the engine which is a very rich mixture. Make sure the choke sysem (circuit) is working / adjusted properly. The fact that you have to pump the accelerator means that either the carbruator is not getting ample fuel during cranking or the carb is faulty. Pumping of the pedal activates the accelerator pump circuit and injects fuel into the bore of the carburetor, which is not supposed to be needed during starting.
All it takes is small amounts of dirt, slug, varnish or bad gaskets within the carb to restrict fuel flow through the idle/low speed jets.
All that technical crap-o-la aside, Do these first before condeming the carb.
Make sure you have unrestricted full fuel flow from the tank to the inlet of the pump. Test the pump with a tester for correct pressure and flow during cranking.(replace if weak)
Overhaul/Adjust the carb.(or replace if extremely worn).

Thanks you guys

Symptoms of a bad fuel pump would be running out of fuel during acceleration. The carb should still have fuel in it when trying to start even with a weak pump. If you can pump it 30 times and not flood the engine, I would guess the fuel bowl is empty from an internal leak or the accelerator pump is worn. Could also be a combination of the two, pump and carb.
BTW, the fuel filter never will be rid of that air pocket, don't use that as an indication of a problem,
Good luck,
Scott

If you are at idle and you stomp on the gas does it rev up smoothly or does it cough and sputter a little? If it isn't smooth that would be a good indication of a bad accelerator pump.

Sounds like the carb accelerator pump as mentioned plus an internal leak. I have put in a new fuel pump and still don't have a full fuel filter. It has less than 300 miles on it. Done this before and rarely had a full fuel filter. I think 48bigtrucks and carbking are right. My carb drains out at night somewhere and am not able to find where just yet. Its been rebuilt. I started 41 years ago rebuilding carbs and turning wrenches. Have to crank it to fill the bowl then it takes off. Irritating! I wish you well.

A worn, weak fuel pump will not hold a prime to the cauburetor if the check valves are bad. After the engine is shut off the fuel in the fuel line (and filter if installed) which is under pressure will slowly leak back through the pumps internal guts. The only fuel READILY available would be what is stored within the float bowl.
A fuel pump is tested with the ignition OFF during cranking, using a remote stater switch and fuel pump tester. If the pump is weak, it will show up during this test. The internal pump parts are moving at their slowest during cranking, if the pump cannot supply ample fuel pressure and volume during cranking, it absolutely cannot during high fuel demands such as high speed or when the engine is under a heavy load. My bet is, that this pump will not pass the test.
And OH by the way, FYI, the accelerator pump IS NOT supposed to have to be used to supply fuel during start up. The accelerator pump (plunger/spring/check ball/nozzle etc) are components of the ACCELERATOR circuit which is incorporated into the carburetor to minimize lean mixture conditions when the throttle valve is opened suddenly.