I have a 1973 F-100. It runs fine if I prime the carburetor, but If let it sit for a day and don't prime it, it will not start. I don't think the carb is holding pressure overnight. Any ideas?

 

What model carb? Rebuild it if it hasn't been rebuilt during your ownership.

 

Definitely sounds like it's time for a carburetor rebuild. Some recommend every couple years, with today's gas. Don't know how true that is, but when was the carb last rebuilt?

There are some good YT videos to watch, along with the manuals available for free download. It's pretty easy to get up to speed these days. Then take the time to get it setup right and dial the idle and idle mixture in.

 

I don't think your mechanical fuel pump is holding the fuel/ you have a small leak in the line. Do you have a clear fuel filter between your pump and carb? If so and you see bubbles in it while the truck is running you have a leak and its sucking air into the line.
I would first check the fuel lines for anything wet, next would be diagnose the fuel pressure issue (install a gauge after the pump) or just go ahead and replace the fuel pump.
In my 78 it involved unbolting the power steering pump, removing 2 clamps and 2 bolts, clean off gasket. Lube up fuel pump arm, install pump and reverse the removal procedure. Crank till fuel pressure and it ran great until a metal line rusted out then I started sucking air in and the pressure would bleed out.

 

I appreciate all of the responses, I inherited this truck from my grandfather and I'm still learning. I went out to try again and I found that if I pump the throttle around 15 times it will start cold and then if I don't stay on the gas for a bit it will go dead. I looked in the carburetor and the choke is slightly open, I imagine this was from my previous attempts to start it. I'm going to let it sit for a good while to get cold, then if it doesn't start I'll look at the accelerator pump. I am pretty sure that a vaccum hose is missing, last year after putting a new kit in the carb I think we couldn't find one of the hoses for it. It runs well after it starts to heat up but it misses just a little bit

 

Look on the throat of the carb for the LIST #, this will provide the part number so you can get the correct kit. Best to buy a genuine Motorcraft, about $20 or so.

 

I wonder if the the accelerator pump is dripping the gas out of the bowl over night.

 

Well, if you are missing a vacuum line and did not plug off the ports, you are probably running super lean - might address that before rebuilding the carb. Also when it's cold, while looking down the carb throat, pump the gas a few times and see whether you are actually getting any action from the accelerator pump - 15-20 pumps is really high, it should fire up after only a few. If it were mine I would check that all the vacuum lines were intact, check the timing and spark (as someone once said, over half of perceived carb problems are electrical instead!) and then dive into rebuilding the carb.

Probably not entirely relevant, but there was a generation of Rochester carbs which was notorious for leakage from the float bowls - when turned off the bowls would slowly empty, then when restarted cold you had to do exactly what you are doing. Had a '70 Cutlass which drive me nuts with that one! What clued me in was checking the lack of 'squirt' when pumping the throttle.

 

It turned out to be a bad fuel pump, if anyone was wondering

 

Boom, I had the same issue a year ago. That and cracks in the rubber that let air in when running and fuel out when sitting over night

 

Thank you for your help. That was really getting on my nerves pouring gas in the carb

 

Just for grins and chuckles, smell the oil - pull the dipstick and take a whiff. If it smells somewhat like gas, change the oil and filter right away. Gas in the oil will wash yer cylinders and screw up yer berrins. Don't ferget the ZDDP with the oil change.

 

It smells good to me, no gas smell. Does the ZDDP really help? I have heard it protects the cam but not really sure what it does

 

On engines like ours it helps reduce the friction between the cam and the lifters. ZDDP causes issues with catalytic convertors so many modern oils have very little ZDDP in them, so running that low-ZDDP oil will ruin your cam at a much higher rate than you will want. Some folks add it as an additive (and it is critical when breaking in a new cam!) but for general purposes, just use an oil rated at about 1200 ppm and you should be OK. The following link has a lot of good info in the first several pages(it loses focus a few pages in)

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