The Stovebolt Site Forums The Shop Area Engine Shop Electric pump for priming carburator

It's common for modern gasoline to evaporate out of the float bowl as our older vehicles sit for a while. I have that issue with both my '38 and my '53. I took steps to remedy that with the '53. This is what I did. I bought a 6v, low pressure, electric fuel pump and installed it per the attached schematic I created. There are in-line pumps that are supposed to allow the mechanical pump to pull gas through them when they aren't being used. The pump I bought had more resistance to the passage of air as I tried blowing through than I was comfortable with it so I set mine up in a bypass circuit. The pump is connected via a momentary switch hanging under the dash, below the ignition switch and wired to be hot only when the ignition switch is on. My '53 has an existing in-line filter just outside the tank which is represented in the schematic. When the momentary switch is activated, the electric pump sends fuel through the mechanical pump, to the carburetor, refilling the float bowl. It is prevented from entering a feedback loop by a one way valve installed just ahead of the existing filter. When the engine starts and is running the fuel, pulled by the mechanical pump, takes the path of least resistance which is through the filter and one way valve. I used 5/16" line and fittings. The line I used is ethanol resistant, high pressure rubber fuel hose. The first test was this morning's cold start and it works as planned. Hopefully the days of long cranking times and/or hand priming the carb are over.

Might improve the situation and perhaps simplify with these few ideas.

1- Connect the electric pump after the filter, that way fuel to it is filtered.

2- Skip the check valve and instead connect the electric pump in parallel with the original fuel pump. The original fuel pump has two check valves already. With the pumps in parallel you don't need to add another check valve (in your drawing) that is also a further restriction in the suction line for the primary pump.

The electric has a filter attached. Not sure about what you mean by putting them in parallel. Using the highly scientific "blow" test, there's little to no restriction in the one way valve I used.

The two pumps would be in parallel in your picture if you substituted the original fuel pump for the check valve.

Nothing wrong with how you have it. I tend to look for simplicity and reliability and fewer parts usually satisfies both.

Typically, there is no issue running the electric pump in series (in line) with the mechanical pump. If either fails the other can still function and fuel flows through both fine, even when the electric is not energized. And, the electric can be selected to run by switch only as needed. There really isn't any reason to parallel connect the pumps as shown in the schematic (which will also work fine). The downside of either configuration is that if the mechanical pump diaphragm ruptures, fuel can potentially flow into the crankcase when the electric pump is in operation. That is true in either case, as shown in the schematic, or the simpler inline configuration. A low pressure 6V pump inline with the mechanical is a good configuration, IMHO.

On my 39 I have a glass sediment bowl that I can clean coming out of the gas tank. It also has a shut off valve. From there the fuel line goes to a low pressure 6v in-line fuel pump mounted inside of the frame rail on the passenger side. From there the fuel line goes to the mechanical pump. The mechanical pump also has a glass sediment bowl on it. From there the gas lines goes to the carburetor. I have an electrical switch under the dash to turn the electric fuel pump on or off. I use the electric pump if the truck has been sitting for a while. You can tell from the sound of the electric pump when the fuel bowl on the carburetor is full. I then turn off the electric fuel pump and proceed to start the truck. Fires right up. I have had occasion to experience vapor lock in extremely hot weather. Flip the electric pump on and problem solved. The sediment bowl under the tank works very well filtering the fuel coming out of the tank.

Rick

My intent was to run it in series, letting the mechanical pump pull gas through the electric. The reason I chose to run it the way I did is, when I blew through the electric pump (again, a highly scientific test ), there was enough resistance that I wasn't sure that was the right way to go so I set it up the way I did. The only additional restriction to the mechanical pump is that from the one way valve and that's basically nil.