Stalling out while driving

[aphaynes]

Ok, new issue that I assume is carb related but I am to far from being any type of expert to know for sure. I had the truck out today (1965 GMC 1000, 305E, stromberg carb, for those who don't know me)and it drove fine on two trips. Then the third trip...to come home...it stalled out while driving down the road. I limped it back to a safe place and this is all I know...

When it does stall out, it typically cranks right back up, with the choke pushed in, after sitting for a minute or two.
However, after multiple restarts to close together (not waiting a minute or two), it will only fire up for a second, but with the choke pulled out instead of pushed in, at which time it revs up for a few seconds then dies...which seems backwards for the choke being pulled out.
Now, on the restarts where I let it sit a minute or two, it fires up with the choke in (70 degrees today) and idles indefinitely (I let it idle for a good 20 minutes at one point) with no abnormal behavior.
Once I start to drive it, best case is about a 100 yards before it has had enough and dies again.
Fuel filter looks good and a neighbor at the old house (that I was trying to move stuff out of today) sprayed it with carb cleaner and blew it out with a compressor just hoping to help the situation. Fuel Pump seems to be getting plenty of fuel to the carb...at least for indefinite idle.
We were both left confused as to the actual source of the problem, so he brought me home and the truck sits loaded with stuff at the old house.

Any tips or advice?

[TJ's GMC]

I talked with a buddy of mine on a similar issue like that and here is what he said, "Typically those fuel pumps when they go bad will supply enough fuel for an Idle, but when you go to drive and the demand for fuel increases they can't keep up." Sounds to me like a bad fuel pump. Wouldn't surprise me either. Getting it to run On choke is a sign of a lean condition. Could also be some blockage in the fuel line....hole or crack in the line.

[Ed Snyder]

Originally Posted by TJ's GMC

I talked with a buddy of mine on a similar issue like that and here is what he said, "Typically those fuel pumps when they go bad will supply enough fuel for an Idle, but when you go to drive and the demand for fuel increases they can't keep up." Sounds to me like a bad fuel pump. Wouldn't surprise me either. Getting it to run On choke is a sign of a lean condition. Could also be some blockage in the fuel line....hole or crack in the line.

I had similar issues one time too, but it turned out to be crud being sucked up against the sock at the end of the fuel pickup tube in the fuel tank. Evidently at low fuel demand (idle) enough stuff would fall off to keep the engine running, but stepping on the gas would suck the stuff back up again.

If replacing your fuel pump doesn't fix the problem, you might check out what's sitting in the bottom of your fuel tank.

[aphaynes]

Thanks for the suggestions. I was taking a wild guess and thinking a float issue, but I will start with the fuel pump then investigate the tank. Thanks again!

[AZKen]

If you can find and install a pump, that would be a good move as said. Normally you would do a fuel pump flow test. Unhook line at carb and let it into a container during cranking. Need to see a strong steady flow/pulse for about 10-12 sec. Should fill up a water bottle PDQ. This is done with coil center wire taken off for safety. If it's weak or not steady flow then it's a fuel delivery problem. Pump on back to tank, as said. You also want to see down carb throat for squirting gas as throttle actuated. (not running/not cranking)

If test fails
1. Pump
2. Clogged/collapsed rubber line
3. Clogged fuel filter
4. Clogged pick up tube at tank
5. Gas cap not venting

Test is good
1. Carb
2. Vac leak
3. Bad gas
4. Coil
5. You don't want to know

[aphaynes]

Originally Posted by AZKen

If you can find and install a pump, that would be a good move as said. Normally you would do a fuel pump flow test. Unhook line at carb and let it into a container during cranking. Need to see a strong steady flow/pulse for about 10-12 sec. Should fill up a water bottle PDQ. This is done with coil center wire taken off for safety. If it's weak or not steady flow then it's a fuel delivery problem. Pump on back to tank, as said. You also want to see down carb throat for squirting gas as throttle actuated. (not running/not cranking)

If test fails
1. Pump
2. Clogged/collapsed rubber line
3. Clogged fuel filter
4. Clogged pick up tube at tank
5. Gas cap not venting

Test is good
1. Carb
2. Vac leak
3. Bad gas
4. Coil
5. You don't want to know

Thanks! ...though that last one has me worried.
Sadly it could not have picked a worse time to act up...after 2+ years of running good. To much going on right now. Hope to find the culprit quickly and get moving again.

[AZKen]

I'm sure you will fix it soon.

[Clarke]

I had a similar issue a couple of years ago and I'm still running stock carb/etc. It would idle for long periods and I could cruise around at lower speeds, but highway speeds would cut out and/or die. The cutouts were not sharp like electrical; they were like running out of gas.

I checked all the items noted above and after I successfully bribed my better half to crank the engine while I had the fuel line from the carb in a clear jar, the low fuel volume and lack of consistent flow, convinced me the mechanical pump was bad. I swapped the pump out and it fixed the issue.

Just FYI. Good luck.

[aphaynes]

Originally Posted by Clarke

I had a similar issue a couple of years ago and I'm still running stock carb/etc. It would idle for long periods and I could cruise around at lower speeds, but highway speeds would cut out and/or die. The cutouts were not sharp like electrical; they were like running out of gas.

I checked all the items noted above and after I successfully bribed my better half to crank the engine while I had the fuel line from the carb in a clear jar, the low fuel volume and lack of consistent flow, convinced me the mechanical pump was bad. I swapped the pump out and it fixed the issue.

Just FYI. Good luck.

Thanks. Looks like I will have to order one. I can only find "universal" mechanical pumps locally. I never like the term "universal".

[jrmunn]

AP - I have driven my 64 1500 with a 305 V6 for over 30 years (more and less, less now), and the only time it behaved as you describe is when the small ceramic type filter at the carburetor was getting plugged up. If you have the original carburetor and this is your only filter, I would start there because it the least expensive possibility. This started happening as the truck (and gas tank) aged, and was solved with a larger in-line filter that gets changed when I think of it. I have had several fuel pumps go out in various ways - more often lately because old pumps don't seem to like the new gas. Usually, the truck just dies and won't start more than once while it uses up the little gas left in the carburetor. But one time, the diaphragm sprung a small leak that was spraying fuel out the small vent hole. I knew something was wrong because the truck was using a lot of gasoline, and I was lucky that it didn't catch fire or blow up. Changing the fuel pump takes about 15 minutes with some experience, and I carry a spare. If all else fails, check the points. Burned or eroded points can cause many different symptoms.

JRMunn