The Stovebolt Site Forums The Shop Area Engine Shop Where to place 6v fuel pump

1942 235 no pressure from mechanical fuel pump, put on another pump off the shelf, but have no history that this one ever worked and reads little or no pressure either. Ordered new mechanical fuel pump from Chev's of the 40's, but reading about electric fuel pumps and vapor lock, etc. If I get a low pressure 6v fuel pump and want to keep the mechanical pump in place to fill the hole and for looks, where would I place the 6v pump. Between the tank and mechanical pump? Do I "block" the mechanical pump, or will the electric pump push fuel through it wither or not it is working?

I have a Studebaker weasel with an electric fuel pump that is on all the time the key is on, but I am reading here about only turning on the electrical fuel pump on cold starts or if vapor lock becomes an issue. With a non working mechanical pump, any down side to leaving the electrical pump on all the time? I see some with "dead man" safety switches to kill the pump if the motor stops running and can look into those as well.

This is on a WWII G506 Chevy 1 1/2 t military fire truck. Died during parade with what I think is vapor lock but cleaning lines and bowing back through tank and checking fuel filter is not showing any dirt or debris. Checking pressure on fuel pump is showing little or none and no gas flwoing through line disconnected at carb.

Only drive for display and parades and shows, but want this to be reliable. Pretty embarrassing when it died in the middle of a parade.

Any help appreciated. First time poster.

Folks have pushed fuel through the mechanical pump with an electric pump for ages. My concern would be if the diaphragm fails could you push gas into the crankcase? The new mechanical pump would be my choice.

There are countless old trucks still on the road with mechanical pumps which do not suffer from “vapor lock”.
The ones which won’t pump likely have other issues upstream of the pump. A partial or intermittent fuel blockage in the tank will mimic a bad fuel pump

Mostly rubber fuel lines. Rubber from tank to pump, steel from pump to almost carb and short rubber to carb. Disconnect line on tank side of fuel pump and blow back air into tank. Fuel flows out of line like crazy. Connect to fuel pump and with key off, hit starter and no fuel coming out of pump and no pressure when we put a gage on it. Initial issue pump appears to be made in China and glass bowl. We put on metal bowl pump from another 235 that we had on the engine stand, but no history as to it's functionality. Pressure gage vibrates slightly, but no fuel coming out of this second pump.

Will wait for new pump to arrive. I need to stick my finger in the block and feel the cam to see if it is scored or worn and causing poor or no pump from the cam lever.

Electric fuel pump was plan B

Good plan. I didn’t consider the pump cam on the camshaft.

Instead of maybe donating a finger to the project, may I humbly suggest using an inspection mirror and a bright flashlight to inspect that pump lobe? There's a way to rig a dummy pump with the guts removed and flow gas through it on the way to the carburetor to eliminate the possibility of oil contamination, and use an oil pressure sensing switch to turn the pump off in case the engine stalls.
Jerry

Even prior to the cam test, one could disconnect the fuel tank from the pump, and connect a temporary tank, such as an outboard marine tank.

This would confirm/deny possible intermittent issues with the fuel tank.

Jon.

Installed new fuel pump and engine starts fine, but gas is exploding out of the carb. PSI is 3.25 coming out of fuel pump. Presume carb was weak and old fuel pump was weak and they both limped along until the fuel pump gave up the ghost. New fuel pump is revealing bad gaskets and seals on Carter W1 carb. So, now it is carb rebuild time. Looks like I can get away from not having to install electric fuel pump.

Rebuilt Carter carb, reinstalled and truck runs fantastic. So, new metal bowl mechanical fuel pump and rebuilt carb and waiting for hot summer day to see if vapor lock becomes an issue. So, no electric fuel pump for now. But will keep in stock for test runs or future needs.

Just curious, I'm no mechanic, but has anyone rigged some sort of Y fuel lines with valve at the Y to run off mechanical fuel pmp but then switch over to electric and throw the valve to allow a separate fuel stream?

A simple manual selector valve for multiple fuel tanks could be set up that way- - - -providing fuel input to the mechanical pump in one position and to the electric pump the other way. Most of those valves are designed to mount under the floorboard with the selector handle accessible to the driver under the seat. Some valves have an "off" position which could act as an effective anti-theft device.
Jerry

SignsUp, if I understand the intent of your question, in order to have redundant electric and mechanical pumps, you don't need an either/or setup. An electric fuel pump can be installed near the gas tank, and the output run to the mechanical fuel pump as normal. Fuel will flow through the electric pump, even if it is not turned on. Likewise, if the mechanical pump should get weak, the electric pump will push/flow fuel through the mechanical pump to the carb, just fine. This can be useful, since the electric pump (if controlled by a manual switch) can be used to prime the fuel system after a long rest, or to aid hot starting, etc. Here is a lengthy piece by Deve that describes what I am talking about (scroll down to "Augmenting Your Existing Mechanical Pump").


One thing to keep in mind, if the mechanical pump diaphragm should fail, it is possible for the electric pump to introduce fuel into the crankcase. Something to think about.

Hope this helps!