i need help. have a "56 thunderbird with a mid-60"s ford 390 engine w/ 4 bbl holley. just had engine completely rebuilt and everything else is new: carb, distributor, electric fuel pump, fuel tank, etc. problem: car stalls and dies after a few minutes of driving. generally restarts after waiting about a half hour, but not always. have a fuel filter with clear bowl in fuel line just ahead of carb. the bowl is usually about 2/3 full of fuel, but general appears empty when the car stalls. after waiting a while, the bowl refills and the car restarts. the problem is driving me nuts and two mechanics are out of ideas. any ideas?
Sounds like the float is hanging up or misadjusted such that the needle valve isn’t reliably allowing fuel into the bowl.
Or… fuel pressure regulator?
Once it restarts does it run fine or is the process repeated? Is the Holley carb a factory unit or aftermarket?
There are several ways this could go and which involves vapor lock or a non-vented gas cap.
the process generally repeats itself and the carb was a new aftermarket unit.
X2 ok4450. Does it do the same thing with the gas cap removed?
Sounds like a restriction in the gas tank. Disconnect the gas line ahead of the glass bowl and run the line into a jar. Energize the pump to check the flow and pressure (should be about 5 psi).
Did this car originally have an electric fuel pump, or is that a recent addition? It does sound like the fuel isn’t travelling fast enough from the pump (presumably in the tank) to the carb, and the symptom is the fuel filter is empty, which starves the engine of fuel, and it stalls. My first suspicion is that you have a defective electric fuel pump, or the power supply to it. The other explanation , less likely, is that the carb inlet needle valve is jamming open, allowing too much gas into the carb, which could also stall the engine and empty the fuel filter. I’ve never had that problem, but on my carb’d truck, the needle valve sometimes sticks shut and the engine won’t start, and I have to remove it and fiddle with it to get it working again.
I’d try loosening the gas cap first, see if it might be a plugged vent. Pretty sure this came originally with a mechanical pump, are you sure the pump is the right pressure? Where is it located?
it’s not the gas cap; I’ve driven it with the cap off and it still stalls. the electric fuel pump is not original, but it’s new and the right pressure and located next to the fuel tank. I’ve just had the car started and idling in the driveway; after about 10 minutes it died, the fuel filter bowl was still about 2/3 full and when I went to restart it, it only ran for 10-15 seconds before dying again. what a mystery.
Do you have the original fuel pump from the 390? Why did you put in an electric pump?
I assume by fuel filter bowl you’re referring to a sediment bowl with the little glass jar?
Seeing as how it has an electric fuel pump, the fuel pressure is not too high is it? Excessive pressure will sink the float in the carburetor.
A failing ignition coil can also cause a problem like this.
Check the routing of the fuel line. From the tank to the firewall make sure it isn’t anywhere that heat builds up. In the engine bay wrap the fuel line with insulating material. If this is a vapor lock issue that should fix it.
I’d also take a look at the new fuel pump. Test both the pressure and flow rate. Something is restricting the flow. A kink in a fuel line, a crimped connector, debris in the tank, or perhaps a defective pump. I’d disconnect the fuel line as close to the carb as you can. Put a hose on the end running into a gas can and turn on the fuel pump. The flow should be so strong you have to hold onto the hose to keep it in the can.
Since the 390 used an OEM mechanical fuel pump - an electric pump replacement must be a low pressure pump. I think about 5 psi. A very different animal from a fuel pump on a fuel injected motor.
I’d tee in a fuel pressure gauge next to the carb and see what it’s getting as the engine dies.
Disconnect the fuel line from the carb and monitor the flow-rate from the electric pump. It should provide 2 gallons a minute, nice and steady with no bubbles or air coming through the line. Also, somewhere in the coil hot wire will be a voltage dropping resistor. In Fords it can be a length of resistor wire inside the engine harness. But it’s there somewhere. If it fails, you will lose your spark…It can come and go with heat and cold…Next time it quits, check for spark.
Most Holly carburetors have removable plugs in the float bowls so you can monitor and set the float level from the outside…The fuel level should be at the bottom of the threaded hole. Have a fire extinguisher handy…
Old car, old school troubleshooting. First step, when it dies, immediately open the hood and remove the top cover of the air filter, then actuate the throttle a few times to see if the accelerator pump is squirting fuel into the throats of the carburetor. Assuming a good accelerator pump since it is a new carb, if it doesn’t squirt any fuel, then it is out of gas. You can’t go by the fuel filter.
If you smell gas, the inside of the throats are wet with gas before actuating the throttle, then you probably have too much pressure from the fuel pump.
Are you sure there is not a 2nd fuel line filter installed where the fuel line goes into the carb ? Had the same situation on my 59 when I bought it. There was a stone filter inside the carb that was blocked. Car would run then shut off after you revved it to 2500 rpm. Let it sit and there was enough fuel pressure in the line that would get past this partially blocked stone filter and she would start right up and repeat the situation.
It also had a glass filter in the fuel line
A heat-soaked coil will do the same thing. The fuel issue may be a red herring. When it stalls, check for spark. Also, as mentioned, check the ballast resistor. It can also go bad.