need help from my fellow Ford community... I recently changed the fuel filter in my 78 ford f150 since it had gunk in it and I could see through the clear plastic filter. I replaced with a new one. When I turn on the truck it starts fine and it stays on while I am pressing the gas pedal. However, when I stop pressing the gas pedal, it turns off. This had never happened before. What should I troubleshoot first. Thanks in advance for the guidance.

 

As a starting point, consider removing the fuel filter again and see if that filter is already partially plugged.

Don't forget to check if what comes out might be contaminated with water.

 

I changed the fuel filter, cleaned the hose that goes from fuel filter to carb, and cleaned the carb. There was a little bit of gunk in the hose. I ended up with same result - truck turns off once I stop pressing gas pedal

 

When it quits running shut key off, remove any spark plug and let us know if it was wet or dry. If wet flooded engine , if dry carb idle system might be -plugged.

Does this problem happen if the air cleaner is off ?

 

it happens under both conditions, air cleaner on and off. However, I did notice that when I place my hands around carb - kind of like covering it - it tends to stay on even though I am not pressing the gas pedal. Doing that looks promising but then when I stop covering it, it turns off again.

Thinking about replacing fuel pump in case it got plugged as well.

 

Before replacing the fuel pump, think about this. What the fuel pump is sending up to the carburetor is sufficient provided too much air is not allowed.
By restricting the amount of air, by restricting with your hand, tells us not enough fuel is getting through the IDLE system of the carb.
Replacing the carb is not necessary, but the carb might need to be cleaned out and this could get a little hairy if gaskets get destroyed.
One thing you might try , if it has a manual choke, pull the choke out all the way at idle. This will create a strong vacuum in the venturi (throat) and just might pull the 'stuff" out of the idle passage which is just below the lower butterfly in the carb.
It was mentioned that replacement carbs are available on ebay.

 

I put a new fuel pump in and new fuel hoses with no luck on the outcome. It does exactly the same thing... turns off when I stop pressing the gas pedal.

 

Did you change any adjustments when you cleaned the carburetor ?

Because this goes back a bit, I didn't think about it, but is the carb a single barrel, 2 barrel or 4 barrel ?

If the idle mixture screws were moved , it could be a simple adjustment that might be all it needs.