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What would cause the fuel to drain back into the tank...

Metal Twister

Metal Twister

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My guess this is what is going on? Every morning I need to pour a little fuel into the carb to get it lit off. Once started it runs ok but occasionally seeme as though it wants to run out of gas after setting at idle for awhile. No wet fuel lines so i wouldnt think there would be an air leak... any ideas.:waytogo:
 
Bad fuel pump maybe.
Next time you turn it off for the night, rev it up, let it run like that for a few seconds and then take your foot off the gas and shut it down as soon as it idles down.

If your fuel pump is going bad, its not pumping enough at idle to keep the fuel bowl filled.
So, its almost dry when you turn it off.
Then its dry the next morning, plus at cranking speed, its not pumping at all so it never fills in the morning.

BUT: Before you do any of that pull the dipstick and look for a too full condition or a gas smell in the oil.

The pump can fail with a bad valve, which just keeps it from pumping right, or a hole in the diaphragm which can let it pump gas into the crankcase.
Which dilutes the oil and ruins the bearings.

If the oil is too full, or smells like gas, DO NOT run the engine again until you have changed the pump, the oil, and the filter.......
 
Which carb?

Q-jets are notorious for leaking well plugs, which will leave the float bowl dry in the morning.

The idle issue would seem unrelated. That is assuming too little fuel, as opposed to really bad leaks richening it up too much.
 
The fact you say it runs funny to me sounds like a weak fuel pump. Might have a bad seal in it. Is it mechanical? If so its a 20 min job to take the 2 bolts out and a new one costs like $25 from a parts store.
 
Thanks guys... As always you have given me a few directions to start checking out. It is a mechanical pump and Q jet carb. I have a few extra fuel pumps so I will throw one on and see what happens. Thanks again for the help. :bow:
 
If you try to test the pump, there is one thing that will sneak by you.
Most manuals give a flow rate.
So many ounces in so many seconds.

In 99% of the times, if it passes that, its good. Its that other 1% that will sneak up and bite you.
It needs to pass a deadhead pressure test too.

I worked on one that ran great, idled fine, but would drop dead on you when you tried to pass someone.
Tested the volume flow twice, rebuilt the carb, no good.

Take it out on the highway, punch it to pass, and it would just run out of gas about halfway past the car.

Finally rigged up a pressure setup, and it had almost no pressure. New pump cured it.
I ate the core, because I wanted to know what the heck was going on.

Turned out the intake valve had popped out of its socket. It would flow enough all day long, but did not develop any pressure.

After that, the few times I have tested pumps, I have always done both flow and pressure.

Of course, most times with the cheaper pumps, I just toss a new pump at it.
 
Gut feeling is that you guys are spot on... I will check it this evening and let ya know whats I find! Thanks again :waytogo:
 
So I start going through my extra parts and find a couple small block chevy fuel pumps. But these are different? They only have 2 ports. One is an inlet from the tank and an outlet to the Carb. The existing pump looks to have a return line hooked up to it? Can I drop the return line and use one of these old pumps?
 
Uhh, what year truck, what engine? My '74 350 has only the two ports, hard line in & rubber out.

I think the '74 454 has three, though, one hardline and two rubber.

-- A
 
dremu said:
Uhh, what year truck, what engine? My '74 350 has only the two ports, hard line in & rubber out.

I think the '74 454 has three, though, one hardline and two rubber.

-- A
Click to expand...

The engine I just put in is a crate motor and the best I can tell its 1984 or eariler. The vehicle is a 1977 so its plumed with the line but I never used it with the old motor? Think the 3rd tube is just a vapor return line and Im thinking I can just use one of the older pumps and let the vapor go through with the gas.:dunno: LOL... Hell I dont know, must be a smog thing? Might be a good thing to know if you get stuck somewhere wheeling and need to borrow a fuel pump? Can ya just run the old style in place of the new one?
 
For testing purposes, I don't see any problem. The return line is open to the tank though, not a good idea to vent gas fumes into the engine bay, not to mention junk getting into the line, etc.

I'd test it that way, if problem is solved, go buy the right pump.
 
dyeager535 said:
For testing purposes, I don't see any problem. The return line is open to the tank though, not a good idea to vent gas fumes into the engine bay, not to mention junk getting into the line, etc.

I'd test it that way, if problem is solved, go buy the right pump.
Click to expand...

Yeah I think your right, If it can get me to the parts counter it will be worth the effort. LOL Plus I will know for future wheeling trips to Mexico... :thumb:Thanks
 
Mn o man this thing is kicking my ass. I threw a new fuel pump on and same thing. So I decided to try an electric pump and still no change. I got under the thing and got up close to the hoses between the body and tank and there is some moister above the tank so Im guessing I have a pin hole back there. Looks like tomorrow night will be new hose night. Oh well gotta go watch the Chargers. I also threw a new module in the HEI... just kinda hoping.:rolleyes: I will let ya know if the hose makes a difference tomorrow night. thanks again for all the help, its appreciated. :waytogo:
 
It is the fuel bowl plugs in your q jet. It allows the carb to leak into the intake leaving you high and dry in the morning.
 
Metal Twister said:
The engine I just put in is a crate motor and the best I can tell its 1984 or eariler. The vehicle is a 1977 so its plumed with the line but I never used it with the old motor? Think the 3rd tube is just a vapor return line and Im thinking I can just use one of the older pumps and let the vapor go through with the gas.:dunno: LOL... Hell I dont know, must be a smog thing? Might be a good thing to know if you get stuck somewhere wheeling and need to borrow a fuel pump? Can ya just run the old style in place of the new one?
Click to expand...

I believe that 3rd line is to keep the fuel circulating/cooler and avoid vapor lock.
 
1-Feed from tank
2-Feed to carb
3-Return to tank from pump

If there are 4 fittings I could see a vent line being one of them, although that is done through the tank.
 
dyeager535 said:
1-Feed from tank
2-Feed to carb
3-Return to tank from pump

If there are 4 fittings I could see a vent line being one of them, although that is done through the tank.
Click to expand...

Yah i was referring to the lines from sending unit not the pump. Was reading it wrong. My bad.
 
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