I am building a 1936 Chevrolet pickup and it has a 261ci straight six with 3x2 Stromberg carburetors and I am installing an inline fuel pump and my dilemma is that the pump just keeps pumping when I have just the key on and so therefore it just keeps filling the bowls and intern just keeps dumping fuel into the engine which is obviously not safe for one but not good for the engine, so I'm trying to figure out a way to design or if it already has been done, a auto shutoff switch which works when it reaches 3 to 5 psi, like most modern vehicles there's are ran from the ecu, well this one definitely doesn't have one so yeah if anyone could help me out or point me in the right direction it will be much appreciated..

 

I am building a 1936 Chevrolet pickup and it has a 261ci straight six with 3x2 Stromberg carburetors and I am installing an inline fuel pump and my dilemma is that the pump just keeps pumping when I have just the key on and so therefore it just keeps filling the bowls and intern just keeps dumping fuel into the engine which is obviously not safe for one but not good for the engine, so I'm trying to figure out a way to design or if it already has been done, a auto shutoff switch which works when it reaches 3 to 5 psi, like most modern vehicles there's are ran from the ecu, well this one definitely doesn't have one so yeah if anyone could help me out or point me in the right direction it will be much appreciated..

Sounds to me like the float valves on the carburettors are not working.

 

Sounds to me like the float valves on the carburettors are not working.
Reply:

Good call I will check into that, cause by right when they close no fuel should come in I knew that, but yes they are good, I think maybe the added pressure could be causeing the fuel to pass the float, Stromberg carbs use very low pressure to work like 2 or 3 psi, and the pump I have is only max 6 psi, the reason for the electric pump is one aesthetics and that I'm running three carbs..thanks for the reply.

 

I have a 1972 Sunbeam Rapier, so I don't know how much Strombergs changed in 36 years. Mine has a mechanical fuel pump operated by a lobe on the camshaft, so if the engine is running there is no chance of disabling the fuel pump, so the float valves have to do their stuff.
The float operates a needle, and it is susceptible to contamination which keeps the valve open.

 

Sometimes the Float-Needles in the Carburetor(s) can be overwhelmed by too much Pressure,
they should never see more than around ~3-PSI according to the Stromberg-Factory-Specifications.

An inline-Fuel-Pressure-Regulator is highly recommended.

The best type of Fuel-Pressure-Regulator is the type that recirculates excess Fuel back to the Fuel-Tank,
this arrangement will prevent any problems with the Fuel possibly becoming over-heated by the Fuel-Pump.

What is the Brand and Model-Number of your Fuel-Pump, and exactly where is it mounted on the Truck ?

Does your Truck have a proper Fuel-Filter ? there should be a Filter before, and after, the Pump.

Is your Fuel-Pump excessively noisy ?

I can help You with Parts selections and arrangements if you're not sure how to go about this.
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I have used these on several small engines instead of cobbling up something to make the pulse pump work.
https://www.autozone.com/fuel-syste...3-5-psi-electric-gas-fuel-pump-42s/732036_0_0

There is one model that is supposed to be between 2 and 3 psi, but I didn't look for the exact part number.

 

If you have dirty fuel, debris can prevent the float valve from fully closing. I find old vehicles need a tank steam clean and flush, and always a fuel filter before the pump and carbs. Or the floats are jamming/hitting a gasket etc. or have leaked fuel in them.
Overfilled float chamber fuel should spill over inside the carb ports - compared to runaway idle.
For that, another thing to check is if the carbs are simply worn out. I have had the throttle-plate shafts worn and wobble, so the throttle plate can't properly close and there was no way to get the idle down.

 

Try googling Kawasaki fuel pump relay. It's a cheap unit that runs the pump for a short period with the ignition is turned on to prime the carbs. When the engine is running it takes a pulsed signal from the low tension side of one of the ignition coils to keep the pump running. If the engine stops for any reason, the pump stops until the ignition is turned off and the engine restarted. Lots of motorcycles have this safety feature. You will fine a wiring diagram with a bit more web searching.

 

With the electric fuel pump you can have a return line back to the tank!! This allows holding a constant fuel pressure at the carbs, or for the injectors. It ain't rocket science, folks!!
It also is not new. Recirculation of fuel back to the tank was one way to beat the dreaded VAPOR LOCK problems that some cars had. There was/still is, a pressure relief valve set to hold the specified pressure at the carb inlets.

It is also used for the "funny" diesel engines in some "funny" heavy armored vehicles that can go really, really, really fast. Recirculating the fuel to keep a constant feed pressure at the injection pump from idle speed up to red line speed.

 

Pretty much all diesels now recirculate fuel back to the tank except for your small mechanical injection engines. Common rail systems have done it since they were first developed. The problem with recirculation is you have to add a second line to the tank if it doesn't already exist. It's not impossible, but it's not exactly a walk in the park either.

Another option could be to use an oil pressure sensor designed for a light to operate a relay. Since the sender would be closed at no oil pressure it would power the relay making the normally open contact active. When the engine has oil pressure it would open the sender switch which will drop power to the relay coil and the normally closed contact would be active. Connect the pump to then normally closed contact of the relay. Of course in the event the relay or sender fails you would be pumping all the time, but normally that will take years to happen.

 

Pretty much all diesels now recirculate fuel back to the tank except for your small mechanical injection engines. Common rail systems have done it since they were first developed. The problem with recirculation is you have to add a second line to the tank if it doesn't already exist. It's not impossible, but it's not exactly a walk in the park either.

Another option could be to use an oil pressure sensor designed for a light to operate a relay. Since the sender would be closed at no oil pressure it would power the relay making the normally open contact active. When the engine has oil pressure it would open the sender switch which will drop power to the relay coil and the normally closed contact would be active. Connect the pump to then normally closed contact of the relay. Of course in the event the relay or sender fails you would be pumping all the time, but normally that will take years to happen.

Reading post #2 and #1, the complaint is that the fuel delivery pressure is forcing the float valves open. THAT sounds like simply excess pressure for the required flow. Thus my suggestion for a return line. Why else have a high flow, high pressure pump?? Unless it was the only one on hand! Big NEWS!! Not all fuel pumps are the same!!
It might, possibly, work to put a resistor in series to drop the pump speed and pressure. Or maybe it might not.

 

We still don't know what type of fuel pump this is.
I've used (Facet) "electronic" fuel pumps, they are just a solenoid plunger and power transistor to make a mechanical oscillator as I remember. They work great and can't make much for pressure and you don't need that for a carb anyway. If they are dead-headed the plunger just stops, it can't move.

 

Post #12 also describes the operation of the engine camshaft driven fuel pump, where the pressure is supplied by a spring, and the driven lever only provides the reset motion. I learned that while I was still in grade school. So it becomes more obvious that the replacement pump may be a positive displacement pump, maybe a gear pump, and that a pressure relief valve for a return to the tank line will be the best choice.
ON/OFF cycling of a pump might possibly work, sort of, but some sort of accumulator in the engine section would be needed to avoid serious supply pressure variation. Evidently none have thought about that aspect yet.
The re-circulation relief valve will only need to be from the discharge side of the pump back to the tank, so it might not be such a big deal to install.

 

How about fixing the carb first? Or using the correct fuel pump?
I think it's dangerous to plumb in a new fuel return line. Very difficult for the long run and many bends - Nobody likes these leaking, it's kind of a flame thrower. I say you don't need a return line for carburetor fuel systems, only TBI/EFI.

Stromberg carbs, the float valve can have problems closing if the fuel inlet fitting is wrong, or with bigger 5/16" lines need special fittings.

For an electronic fuel pump shutoff, key-on they run the pump a couple seconds to prime, and then the mass airflow sensor if there is airflow, will enable the pump on. You could use a tach signal instead but remember cranking may not activate the pump (cranking RPM too slow).
There is also the G-force shock switch inside pumps with a return line, to kill the fuel pump if there is an accident and stop a flame thrower.

Some electric fuel pumps have a pressure relief valve to limit max. pressure. Like Holley 12-801. TS fuel pump many have a problem with that being the reason pressure goes too high.
You can get small fuel pressure gauges people attach to the carb inlet as well to know at a glance. Just measure it.

 

Reading post #2 and #1, the complaint is that the fuel delivery pressure is forcing the float valves open. THAT sounds like simply excess pressure for the required flow. Thus my suggestion for a return line. Why else have a high flow, high pressure pump?? Unless it was the only one on hand! Big NEWS!! Not all fuel pumps are the same!!
It might, possibly, work to put a resistor in series to drop the pump speed and pressure. Or maybe it might not.

I thought I read somewhere it was a low pressure pump already, but after reading through it again I found I was wrong. I guess that is one vital piece of information that has not yet been delivered.

It could also very well be a float / needle / seat issue that has not yet been discovered also.

There are also several varieties of low pressure pumps (see #6 for one of them) on the market also that would make life a lot easier instead of setting up a return line.

If by chance it's a retrofit with an in tank mounted pump then there should already be a return connection that can be used.

Does that about cover everything?

Edit:
I guess since it is specified as an inline pump the comment about an in tank pump doesn't do any good.

 

How about fixing the carb first? Or using the correct fuel pump?
I think it's dangerous to plumb in a new fuel return line. Very difficult for the long run and many bends - Nobody likes these leaking, it's kind of a flame thrower. I say you don't need a return line for carburetor fuel systems, only TBI/EFI.

Stromberg carbs, the float valve can have problems closing if the fuel inlet fitting is wrong, or with bigger 5/16" lines need special fittings.

For an electronic fuel pump shutoff, key-on they run the pump a couple seconds to prime, and then the mass airflow sensor if there is airflow, will enable the pump on. You could use a tach signal instead but remember cranking may not activate the pump (cranking RPM too slow).
There is also the G-force shock switch inside pumps with a return line, to kill the fuel pump if there is an accident and stop a flame thrower.

Some electric fuel pumps have a pressure relief valve to limit max. pressure. Like Holley 12-801. TS fuel pump many have a problem with that being the reason pressure goes too high.
You can get small fuel pressure gauges people attach to the carb inlet as well to know at a glance. Just measure it.

What the TS asked about was a method to switch the fuel pump off and on to regulate the pressure at the carbs fuel inlet. Sort of like a switcher power supply "buck" regulator.