My engine won’t start if I let it sit for more than 3 days. I have to add gas to the carburetor to get it to fire then it runs great. I replaced the fuel filter, gas tank is full, the fuel pump seems to work fine.
I have a Rochester Quadrajet 4MV. Might my problem be the accelerator pump?
Nope, if the fuel pump is not quickly refilling the fuel bowl, you need a fuel pump. Test the pressure and volume.
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And if the fuel bowl is draining in a couple days, the Q-jet needs a rebuild too.
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Thanks. Let’s assume the fuel pump is ok but the fuel bowel is empty. Should the fuel pump refill the carburetor bowl when the engine is cranked, assuming the fuel pump is healthy and gas tank is full.
Yes, with a few seconds of cranking
Thank you. Sense I don’t have a way to measure my FP pressure maybe I should just replace it and go from there.
I did read that I could also test the discharge flow rate to troubleshoot. Something like 1 pint per 30 secs of cranking the engine?
Correct on the discharge rate. Just be careful aiming the fuel line into a container, you don’t want to spill fuel on the hot engine. I did that once in the 1960’s, and it didn’t end well
Thanks ‘OMG’. Would you happen to know what kind of discharge psi is expected on a healthy pump?
Iirc, and I’m old, so I may not,5 - 7 psi
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Ever drive it up steep hills for long? I had a fuel pump failure that showed first when climbing long steep hills, then as trouble starting. I removed it and worked it manually in a bucket (of water) and it seemed to work, but I reached the point that I couldn’t get my '87 Toyota pickup started until I replaced the fuel pump. I got a new one at the Zone of Auto for $27. It was an easy job.
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Yes Random, that’s happened on my truck as well. I thought it was due to not enough gas in my tank. You’re saying if the fuel pump isn’t putting out enough psi then the carburetor would starve going up LONG STEEP inclines. Makes sense thanks.
There are 2 plugs in the fuel bowl that are notorious for causing that problem.
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I would have to agree with you Sir… That or a cracked casing.
For giggles you could stuff paper towels down past the throttle plate and see if they are soaked with fuel days later.
Also you having to add gas to the carb… I assume this means squirting some down the bores? If so, that is your accelerator pumps job. It gets its fuel from the bowl where said fuel should be waiting for it…till it evaporates or leaks out of a cracked case or those two plugs @Rod_Knox mentions.
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Thanks. I’m sure fuel is leaking out of the carb bowls and it takes a couple days or so to empty.
If the bowl is empty will the fuel pump refill the bowl as I crank the engine, so that the accelerator pump can then take suction normally?
Correct. Your fuel pumps only job is to keep that float bowl full at idle as well as under full load. Your engine runs on what is in the bowl…the float prevents overflow of the bowl. The accelerator pump squirts small jets of fuel directly into the carbs throat to assist starting as well as to get things moving in the engine department so the venturi effect can take over after that…
Your bowl may be full and the accelerator pump cannot get that fuel…or cannot pump it…either way no bueno.
Or your bowl may be empty and if it is the only way it could be thata way is a crack in the carb body or those plugs @Rod_Knox so quietly mentioned.
So you need to ask yourslef, are you a bowl half full or half empty kinda guy? Perhaps that doesn’t matter, but find out which your carb is and solve this issue.
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Well said HB thanks. Solving ‘issues’ like this isn’t my strongest point, but I’m willing to do my best with the resources that I have. Everyone here has helped me a lot and I thank you. I can now make a more educated decision.
I would strongly suggest you suspect the accelerator pump as you did in your first post…
Before you start the engine… look down the carburetor bores and work the throttle with you hand…you should see small jets of fuel being sprayed into the abyss… If you do not… The accelerator pump is your first stop.
The bowl is your second stop… Ironically both can be accomplished at the same time if you are brave enough to take apart the carb.
I still remember my first carb disassembly in my basement when I was about 12-13 yrs old and my mother yelling about smelling gas and me trying to look all confused about it…
Wouldn’t one way to check the accelerator pump be to get the truck running, then see if it pumps? If it does, not the accel pump. I wouldn’t think ‘it runs great’ if the accel pump is bad.
A fuel pump for a carb should be low pressure, maybe even 2.5 PSI.
If the bowl is draining, the first suspect would be those plug leaking as suggested. They used to epoxy them. If you want to test the fuel pump just disconnect it and put a container on the outlet and crank the engine to see if fuel is pumping out. Normally a worn accelerator pump give you a hesitation when you step on the gas.