I'm looking for some ideas on what to check next... I have 1973 F-100 with a 390. A couple of weeks ago, it began to idle rather rough, lacked power and acted like starved for fuel. It has a stock 4300 carb so I thru in a kit. Truck started right up and I thought the problem was fixed. Hah! After running 5 minutes, killed and wouldn't start. Waited for it to cool down and it started right up...ran 5 minutes then killed. I have a Edlebrock 1405 that was running just fine on another truck so I tried swapping it out....same symptoms.

I suspect that the problem is related to the engine warming up. Once warm (not hot), the engine seems starved for fuel. When it initially starts cold, it runs like a champ but then it sputters and dies.

I suspect a vacum leak of some type but nothing external. Thoughts? I'm getting nowhere.

Thanks in advance.

 

What does "nothing external" mean? Time to put a vacuum gauge on it.

 

The 4300 carb and intake manifold have been swapped. No 1973 F100/350 390, nor 1968/72 F100/390 390 came w/a 4V carb.

1974 was the first year the 390 was available with an optional 4V, and thru 1976, it was a Holley 4V not a 4300.

 

I had the "run for a while and stop" problem on mine. The cause was old rubber fuel lines that had gotten soft with age and alcohol to the point they would suck shut. When the engine died and the suction stopped they would return to shape enough for it to start again for a while. A few feet of rubber line fixed it.

An easy diagnostic is to pull the air cleaner when it dies and pump the accelerator. If you see no pump shot that would tend to confirm no fuel. Other fuel problems could be a partially plugged filter or fuel pickup strainer... when fuel is flowing it pushes the debris into the filter, when flow stops enough falls off so it will re-start.

 

Swapping out the fuel line is easy enough. I will give that a try. I suspected all along that the engine was not "original". I'll trying a vacuum gauge if I can keep it running long enough. FYI - started it up today and ran it for about 10 minutes...ran fine for that long then died and couldn't get it to start again. Thanks for the input.

 

At the fuel pump disconnect the hose running back to fuel supply .. Buy about 6ft. of fuel line .. Grab a stool and a fuel can with fresh gas and set it on the stool by the drivers side front wheel well at fuel pump height .. Run the fuel line from the fuel can through the fender well to the fuel pump .. start the motor .. if runs without problems the fuel delivery problem is from the pump back .. If the problem persists then the fuel pump may be suspect then replace it with any filters between the pump and carb .. If the problem still persists we need to look at the carb or the problem is not with fuel delivery .. You need to eliminate the suspected fuel delivery issue first .. Then go from there