fuel pump draining?
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Junior User
Joined: Sep 2008
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fuel pump draining?
I have an anoying problem with my truck that Im hoping to get help with. When my truck sits for more than a week or so, it takes a long time to start. Almost to the point of running down the battery. I have a clear fuel filter and its dry after it sits. Then it takes a ton of cranking before it fills and then a little longer before the fuel gets to the carb. So heres my question: Do mechanical fuel pumps have a built in check valve? And if not, are in line check valves available through the after market? Once the truck starts it runs great and gets plenty of fuel, so I dont want to replace the pump for no reason. Thanks.
BTW The motor is a 79 351W if it makes any difference
BTW The motor is a 79 351W if it makes any difference
Cargo Master
Joined: May 2007
Posts: 2,071
Likes: 36
From: British Columbia
Conventional mechanical fuel pumps have one intake check valve and one outlet check valve. Racing or large industrial fuel pumps may have more than one of each. These will seal for a while with the engine off, but a week's time is a little long for them. They are generally just bakelite discs that seal against a metal seat.
However, if you think about how fuel gets into the carburetor fuel bowl from the needle and seat of the carburetor, you will realize that fuel cannot pass back into the fuel line. This is because the inlet needle and seat are above the surface of the fuel in the float bowl.
Unless you live in a very hot climate, you probably have a fuel leak allowing the carb to slowly drain. Check that there really is no fuel in the carburetor by working the accelerator pump. If there's no fuel, a good way to prime the carb is to pour an ounce or two of gasoline into one of the carb vent holes with a very tiny funnel.
However, if you think about how fuel gets into the carburetor fuel bowl from the needle and seat of the carburetor, you will realize that fuel cannot pass back into the fuel line. This is because the inlet needle and seat are above the surface of the fuel in the float bowl.
Unless you live in a very hot climate, you probably have a fuel leak allowing the carb to slowly drain. Check that there really is no fuel in the carburetor by working the accelerator pump. If there's no fuel, a good way to prime the carb is to pour an ounce or two of gasoline into one of the carb vent holes with a very tiny funnel.
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Thanks guys. I'll try to see if I can find evidence of a leak. If not I'll just pick up a new pump. I cant imagine that a pump would cost much. A couple weeks might be a low estimate. At times it sits for a month or more so the gas in the carb might just be evaporating. I just dont know.
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