Not getting fuel from tank

[Jimbuck49]

I have a 91 C1500 that we just installed a carbed 350 with a mechanical fuel pump. Having problem with the tack, sender and getting fuel to the engine.

We have the return and the vent tubes on the sender plugged. When we hook up to the tank it seems we can not draw and fuel. We tried removing the gas cap to vent but that did not work.

Does a stock mechanical fuel pump have enough sucktion to life fuel the 13 inches?

Looking for suggestions.

Thanks

 

[RichLo]

Are you pulling through the in-tank pump?

You may have to prime the mechanical pump a few times until it starts pulling on its own.

 

[Scooterwrench]

We ran mechanical fuel pumps on airboats where the engine was 4-5 feet higher than the tank with no problems so it's not the 13". I think your problem is that the mechanical can't draw fuel through the electric in-tank pump. You will have to either remove the in-tank pump and install some sort of pick up tube that reaches to the bottom of the tank. If you run the factory inline fuel filter you won't need a screen in the tank.
The other(and best)option is to run the in-tank pump and install a bypass regulator set at 3-5 psi. You should run the vent or you may have a serious pressure build up in the tank that will increase fuel pressure above the limit that the float needle in the carb can hold back.

 

[Scooterwrench]

Are you pulling through the in-tank pump?

You may have to prime the mechanical pump a few times until it starts pulling on its own.

Mechanical pumps are self priming.

 

[someotherguy]

You should run the vent or you may have a serious pressure build up in the tank that will increase fuel pressure above the limit that the float needle in the carb can hold back.

This especially, since the cap will not vent the pressure, by design.

Richard

 

[Schurkey]

I have a 91 C1500 that we just installed a carbed 350 with a mechanical fuel pump...

...We have the return and the vent tubes on the sender plugged.

1. Did you use an engine-driven fuel pump with a vapor-return port? If not, you need a different pump.

2. The truck is built with fuel return plumbing. Connect the fuel return plumbing to the vapor-return port on the fuel pump. Blocking the return is crazy.

3. The vent port on the tank goes to the charcoal canister.

When we hook up to the tank it seems we can not draw and fuel. We tried removing the gas cap to vent but that did not work.

Does a stock mechanical fuel pump have enough sucktion to life fuel the 13 inches?

Are you pulling through the in-tank pump?

...and are you pulling through a plugged fuel filter?

It's not the "13 inches" that's the problem. Might be the filter, might be the pump, might be a plugged filter sock. Might be some combination.

Or, as said...might be that the pump is defective, doesn't have a pushrod, or just needs more time to prime.

You may have to prime the mechanical pump a few times until it starts pulling on its own.

Fill the float bowl(s) of the carburetor. Block the vapor return port on the fuel pump, or clamp the hose. Connect a vacuum gauge to the inlet fitting of the fuel pump. What is the vacuum developed when the engine runs? Does it hold vacuum when the engine is shut off?

We ran mechanical fuel pumps on airboats where the engine was 4-5 feet higher than the tank with no problems so it's not the 13". I think your problem is that the mechanical can't draw fuel through the electric in-tank pump.

Yup.

The other(and best)option is to run the in-tank pump and install a bypass regulator set at 3-5 psi. You should run the vent [to the charcoal canister] or you may have a serious pressure build up in the tank that will increase fuel pressure above the limit that the float needle in the carb can hold back.

Yup.

Mechanical pumps are self priming.

Yes, but not efficiently. They don't pump air effectively, so they don't pump air OUT of the pump. A vapor-return helps somewhat.

 

[GoToGuy]

What parts are still in the fuel tank? What type , brand pump are you using? You do have the rod installed that drives the pump arm? A very experienced person I know forgot that item.