My truck is a 56 with a 292 in it. I put a tank in the back, where a spare tire might go, the pick up for the tank is lower than the mechanical fuel pump. Is this a problem? I know if I use an electric pump I need to have the pump lower than the tank in order to have a gravity prime, is this the case with mechanicals as well? Thanks for your input,
-Doug

 

If the pump is working correctly, it will create vacuum sufficient to pull the fuel to the engine. You may have to crank the engine a while to get the fuel to the carb but it will work. Cars worked this way for years. Disclaimer: I don't consider myself a guru.

 

I am no expert , but I see no problem with your set up . My 53 Pontiac tank is rear and low , with no issues .I run the stock pump , Fuel and vac in one pump , to run the engine and wipers .

 

You don't really need to be a guru, your thoughts and experience are very helpful though!
Thanks
-Doug

 

I'm no guru either, but if you think about it, the fuel line coming out of even the stock tank behind the seat is lower than the stock mechanical fuel pump. Like Ray said, sometimes they have to crank a while. I think it took about a minute for my truck to put the fuel into the carb today after sitting for a couple weeks.

 

The 56 had the tank behind the seat so it was higher than the pump. I must have a weak pump, I'll try a new one.
Thanks again,
-Doug

 

Check the steel fuel line from tank to front of the truck. Anywhere the line clamps to the frame is a suspect area for rust. And of course, check the fuel hose for holes. Any hole at all and it is not going to draw fuel.

 

What Ray said. Check the lines - assume they are crud filled before you start replacing the fuel pump. Ask me how I know...

 

Yeah but where did the fuel line come out of that tank? I know the fuel pumps were lower on those engines, but I still would think it would be higher than any fuel line coming along the bottom of the cab.

 

Mechanical fuel pumps, when the check valves are working properly pull as much vacuum as pressure since the diaphragm pulls vacuum on half the stroke and pressure on the return. Most cars up into the 70s had the fuel tank low in the back under the trunk. f the carb leaks and goes dry when sitting, the check valves in the pump can go dry and stick or fail to seal enough to self prime.

 

All the fuel lines are new and the filter is new. The tank outlet is about 8" lower than the frame rail in the back. I took the pump out and manually maneuvered the actuator arm, it sounded like it was working but that's not very scientific. By the way the fuel line is mounted to the bottom of the frame rail. Thanks for all of your responses, it's going to make figuring out this issue a lot easier. By the way, just finished the Toyota PS conversion, very simple to do even with the body on. Purchased the PS hoses from Midfifty, all of the adapters and everything else needed to make it work were included. Made the job even easier.
Thanks
-Doug

 

So hold the pump, vice preferred, work the arm while sticking your finger over the inlet side and you will feel the suction. If the pump is working, you'll feel pressure on the discharge side.
Edit: If you keep your finger on the inlet side the pump should hold the vacuum for quite a while, minutes or longer.

 

Agree with this, if the pump is in the truck pull the fuel line off the discharge side of the pump to check. Don't trust the carburetor as a stuck needle valve on the float will prevent the bowl from filling.
If no fuel check the filter in the fuel line. On mechanical fuel pumps the clear fuel filters are your best friend.
If no fuel check as described above. If the pump is good and no fuel pull the fuel line from the tank. Often they have a mesh "sock" filter.
One last thing to check, open the gas cap. If you hear a rush of air in you have the tank sealed and air needs replace the fuel on these old systems.
I'm no expert or guru, just old enough to have experienced pre emissions vehicles.

 

Is the tank outlet on the bottom of the tank? Where did you get the tank? Did someone put the gas line into a drain bung? Gas tanks with bottom outlets are very dangerous and illegal in many states, especially if below the bottom of the frame. High centering over something (such as backing up to a curb or running over an expressway alligator) can easily crack or knock the line off the tank, and nothing will prevent it from leaking until dry. Fuel lines should never be below the bottom of the frame. I would also highly recommend rerouting the fuel line inside the frame to protect it. A bottom outlet tank will also plug easily since any debris can easily cover the outlet and/or be sucked into the line.

A combo vacuum/pressure gauge is inexpensive and essential when working on carburated engines and should be in everyone's tool box.

 

I don't trust the plastic filters, especially in the engine compartment. We pulled one off of "BunnyBlue52's" truck the other day, and the plastic looked OK but was squishy, softened over time. There's a reason you won't ever see a clear plastic OEM filter.

I haven't seen it mentioned, but does this mechanical pump have a glass bowl? If so, the gaskets on them are highly suspect and a common leak point.