The Stovebolt Site Forums The Shop Area Engine Shop fuel delivery gremlin ?

I've been working on a 59 Suburban. Got the battery draining problem figured out .I had been sorting out the wiring and found that the wipers didn't work because the wire wasn't hooked up. Hooked it into the fusebox and they worked great. Found out that the previous owner must have disconnected it because it was killing the battery when not running.
My NEW problem is frustrating too. The truck starts up great when cold and runs great until hot. I put a 3/4 inch plate under the carb to keep the gas from boiling. That didn't change the problem. It seems like a vapor lock.But my gas tank is vented. I can get the truck running again if I disconnect the fuel line turn the key to run some fuel through and then reconnect the line. Starts up. My fuel filter is glass so I can see if it's dirty gas. Any ideas would be greatly appreciated.

what engine? what carb? does it have an inlet filter/screen that may be getting plugged?

Bill

The way it responds to your re-establishing flow by venting the fuel line to prime the pump plus some time has elapsed since the shutdown makes me think:
Maybe but not so likely, a small air leak between pump and tank.
Possibly something in the tank plugging the pickup causing shutdown but then clearing itself when the flow/suction has stopped for a while.
A flow test immediately at the time of shutdown would be helpful and a pressure test could be useful.
Fuel flow interruption from "vapor lock" will occour in the pump or before the pump---not after the pump because the vapor would be vented through the carb bowl vent.
Carry a helper with you to help in the test, and be prepared to test the situation at the time of shutdown.
Good hunting

Install a cheap-o type fuel pressure gauge at you filter. If possible mount the gauge where you can see it from the cab ( not in the cab).

If you loose pressure, then look at the pump or tank. A normal pump should be in the 3 to 6 psi range, bur even 1-2 psi is enough to run a engine.

If you have pressure but engine still won't run, look at the carb needle and seat, or carb inlet filter.

With the gauge mounted between the tank and pump, a high vacuum on the gauge and engine not running could one of the following,

(A) the tank pickup is clogged
(B) the rubber or steel line is bad
(C) the tank vent has a problem

A good test is to use a clean fuel jug mounted in the bed running to the pump with new clean fuel line. This eliminates fuel tanks and lines. Dirt in a tank can be tricky, it gets sucked up and plugs off the flow till the engine quits, then the dirt settles back to the bottom till the cycle starts again. It only takes a second for the dirt to fall off the pickup up tube and free up the flow.

Joe

Those of us trying to keep em' running in the 70's saw a bunch of this "sometimes pluggage" on the vahicles of the late 60's-early 70's---mostly GM.
Many times the vehicle would run normally for days and then shutdown on the road only to restart after a short rest.
Sometimes you could make it repeat by making a high speed or load effort like open throttle uphill.
I never found out what had changed in the way the vehicle was made from earlier or later but the plastic gauze type filter on the pickup was at fault and sometimes left a imprint where it was sucked up against the pickup tube.After the suction was interrupted it backed off and buisness as usual.
Sometimes mechanics would blow back with air to clear the situation but the real cure was replacement of the pickup assembly or rip off the filter and install a good inline.

This truck came to me with a 350 in it with an old broken down Roch. mounted to an edelbrock intake. I was hoping to do some miner repairs and use as my daily driver as I worked on restoring it.
So now it's got a new 600 edelbrock carb on it jetted for my altitude (7000) feet.
I took about 4 feet of gas line out of it. The electric fuel pump,which I'm not a fan of,was mounted directly over the exhaust so I moved that to the frame rail away from the heat. This truck had the problem before I did these modifications so I thought that I had cured the fuel problem. I guess I'll try the ideas you guys gave me and I'll let you know. Thanks

Hotshoe, Remember too, most electric pumps are more reliable near the tank to push rather than to suck as the original does.
It may be a restriction issue made worse by pump near the front, hot weather acting on our low boiling point fuel, and the sign of the moon.
A pump near the rear leaves very little place for "vapor lock" to originate.
Good Luck
I'm gone for 2 weeks
See you at Goodwood Revival

Here are the results of my last episode with this truck. Ran it idling until it quit. (until hot)Then I removed the gas line from the carb and turned the key. No gas would pump. Now I don't know if I waited an hour and it would pump through the line or if I had pointed the line down some and drained it a little and then it would pump through. Either way it'll pump gas through the line now and start the truck.
The electric fuel pump is mounted with about a foot and a half of line between it and the tank. Haven't been able to test how much pressure it puts out yet.

Check voltage at the pump, it must maintain full battery with plenty of amps. Its best the use a 30/40 amp relay at the pump and use smaller wire to switch it, then run 12 gauge right off the battery to power the pump. Run a 12 gauge wire for the ground at the same time. Be sure it has a safety switch wired into the oil pressure circuit, and a primer button for easy starting.

Is the pump mounted at a low point on the frame? pretty close to the bottom of the tank level? That might help keep it working.

Was the pump still running when it quit? you could hear it or felt of it?

Try this, run a line from the pump back into the tank and let it run for a while. If the tank is plugging up, it should quit fairly quick due to the high volume of fuel moving.

It could be you just have a bad pump, with the engine running, very little fuel is moving through the pump. With out fuel movement, heat builds shutting it down till it cools.
You can add a regulator to return fuel to the tank to help cool the pump.
Holley regulators are cheap and work good for this. Install a " T " fitting at the pump off the outlet side (pressure side). Run this new line into the side of the regulator then run a line out the bottom of the regulator to the tank (can be 1/4" line). Adjust the regulator for 1 - 2 psi. It looks backwards, but works just fine. Hooked up backwards like this gives full volume to the carb with only a few pounds of pressure drop going to the tank.

Joe