hey i have a 56 f100 that i mounted a mustang tank under the bed and a 390 . when cold or if it has been sitting for days and I go to start it , it takes about 20 seconds of cranking before it will start. after its warm it starts right up. does anyone think that I need a electric pump to solve that?

 

I had a similar problem years ago and it turned out to be a bad carburetor. The gas would leak out of the float bowl and had to refill before starting. You could have something similar going on or possibly a weak fuel pump or even the automatic choke could be out of adjustment. Something may be allowing the gas in the line to drain back to the tank...

 

Might be a bad diaphram in the fuel pump i just has to replace mine. works great now I ordered mine from orielys online it was like 32 bucks. Dont worry if the pump looks different it still works. I does sound like it may be carb related though. take off the fuel line and see if anything pumps out when you crank it that will tell you if it is the pump or not. then go from there.

 

so with a bad diaphram does it work most of the time ? and i assume that would let the gas leak back into the tank?

 

There is a check valve in your fuel pump to prevent drain back to the fuel tank from setting. It likely is bad. If you pull the top off the carb after sitting a few days and the fuel bowl is empty the carb is leaking.
If carb is leaking the engine will have to turn long enough to refill the fuel bowl to start.
One answer is add a electric pump on a separate start type momentary button and push it to prime the carb and then let the mechanical pump run the engine. I have this setup on several vehicles that sit for extended periods of time to save a lot of cranking to get them started after sitting for a few months.