fuel pump losing prime?

my jeeps fuel system seems to lose its prime after sitting more than a few days. then the only way it starts is with someone dumping gas down the carb while i turn it over. then it will start right up with ease. what do you guys think it is my guess is the fuel pump but i have no experience with carburated engines.

 

Unlikely it's the fuel pump if it runs.

More likely fuel is evaporating from the float bowl and it takes a while for the pump to refill it. Any carbureted engine will dry up if it sits long enough, but it dries out faster if the air cleaner is off, or if you use an open element air cleaner, or if the carb gaskets don't seal.

Do you using the factory air cleaner? How about the gasket between the carb body and carb top?

 

Sometimes mechanical pumps start leaking through the diaphragm into the crankcase. Or the fuel line might have a small crack that lets the gas drain back down the line. Mine had cracked and leaking fuel lines. Once replaced it never loses prime.

 

Same thing happening to mine- Over the past year I have replaced the fuel pump, rebuilt the carb (also replaced the float), and have replaced 50% of the steel fuel lines, all of the rubber ones. I think I'm losing prime due to a leak in the fuel lines, but who knows ???? I have to pump and pump the gas pedal, eventually I get gas up to the carb and it'll fire. It's ok for about a day or two, but that's it.

 

Mechanical fuel pumps have check valves. If one is slowly seeping it can allow the fuel in the lines to drain back towards the tank over a period of time, but still produce enough volume and pressure when the engine is running for the engine to run just fine.

 

What year Jeep is it, what engine and which carburetor do you have. I would make sure that the accelerator pump in the carburetor is working first also does your choke work? (most engines don't need a choke to start in the summer if the accelerator pump is working). If you have or can borrow a vacuume/pressure gauge you can test the fuel pump. A good working fuel pump will draw and hold 14" in.hg.of vacuume on the suction side while cranking the engine and produce and hold 4-6 psi on the pressure side, and like the others said an air leak between the fuel pump and the fuel tank can also make an engine hard to start. I have a hand held vacuume pump that I use to test the fuel lines to the tank.

 

fixed it it was just a cracked fuel line.

 

Good deal. I think I'm going to go home tonight and see if I can find the leak in my CJ, assuming that there is one. Also have a leaking master cylinder, or brake line...gotta find out why the front compartment is leaking down. As I recall, the front compartment controls the rear brakes, while the rear comaprtment controls the front brakes, something like that?

 

On my 73 with manual brakes front bowl is for rear brakes, rear bowl for front brakes.