Electric fuel pump to prime mechanical

[Brax601]

I was curious if anyone has put a electric frame mounted fuel pump between the tank and mechanical pump. I was just thinking of using it as sort of a primer pump. Is there any concerns with blowing through the mechanical pumps seals? I have done this to some old hunting rigs that are just ran a couple times a year, but never something I intend to drive a few times a week.

 

[DirtDonk]

I don't think it'd hurt anything, but I don't see the need either.

I think a lot of people used to do it for the reasons you previously did too. But I don't think that I know anyone who did it to a daily, or an almost daily driver. Just doesn't have the same need.
If you're losing prime in just a day or three then something else is wrong. Of course, that "something" could be the new fuels I suppose, in which case a primer pump might help.

As far as damage to the mechanical pump, I don't see anything that would hurt it any more than it would have in the old days of hunting and rock hounding rigs needing it after a winter's sleep or as a backup for when their primary pump failed.
That latter has some potential drawbacks (like leaking through a busted diaphragm) but I don't see the electric pump actually causing the damage.

But a lot has changed with the quality and capabilities of replacement parts over the last thirty years too. So there's that to contend with now.
Are you having trouble now? Or just thinking ahead in case it's a thing?

Paul

 

[75MIKE]

Except for having to pop the hood.

https://www.amazon.com/Ogrmar-Assem...1&keywords=primer+bulb&qid=1620052795&sr=8-10

 

[jckkys]

The mechanical pump is positive displacement type so it needs no priming. Electric fuel pumps are the same. Centrifugal pumps like the water pumps do need priming. To the best of my knowledge, there are no centrifugal fuel pumps. So an additional electric pump is simply redundant. It would be fixing what's not broken. I'm curious what causes you to think the mechanical pump isn't working immediately when the engine is cranking?
Vehicles that sit for long periods will have empty float bowls as a result of evaporation. So the act of cranking has to fill the float bowl/bowls before any fuel gets into the cylinders. An additional fuel pump powered by the ignition switch won't change that. A flow through electric fuel pump on a separate momentary switch could be used to fill the float bowls before cranking. This would make sense for vehicles that sit for extended periods. You could simply press the electric pump button for a few seconds to fill the bowls then crank the starter.

 

[Rustytruck]

I knew someone who used an electric pump to push through a vapor lock condition on hot restarts. I don't know what pump he used or how it was configured. any time is truck wouldn't start on a hot restart he would hit the electric pump until it started. it solved his problem until he sold the truck. I don't know how his mechanical pump drew fuel through the electric pump with the pump off.

https://forums.aaca.org/topic/17406...for-priming-only/?tab=comments#comment-857000

 

[thegreatjustino]

The mechanical pump is positive displacement type so it needs no priming. Electric fuel pumps are the same. Centrifugal pumps like the water pumps do need priming. To the best of my knowledge, there are no centrifugal fuel pumps. So an additional electric pump is simply redundant. It would be fixing what's not broken. I'm curious what causes you to think the mechanical pump isn't working immediately when the engine is cranking?
Vehicles that sit for long periods will have empty float bowls as a result of evaporation. So the act of cranking has to fill the float bowl/bowls before any fuel gets into the cylinders. An additional fuel pump powered by the ignition switch won't change that. A flow through electric fuel pump on a separate momentary switch could be used to fill the float bowls before cranking. This would make sense for vehicles that sit for extended periods. You could simply press the electric pump button for a few seconds to fill the bowls then crank the starter.

This.

I bought my '67 Bronco from the original owner. One of the few changes he made from stock was to bypass the stock fuel pump (left in place to operate the wipers) and install an electric pump on the driver wheel well in the engine bay. Due to being driven irregularly, the electric pump would quickly fill the fuel bowels and the Bronco would start right up. However, due to the mounting location of the electric pump - in the engine bay instead of back by the tank - the pump would regularly run dry (you could hear the dry clicking while driving) and on hot days, the Bronco would just randomly die due to the pump overheating. I finally got sick of it and hooked the stock mechanical pump back up. Now when I go to start the Bronco, it takes forever to get the fuel bowls to fill up. Either that or I have to prime the carb. I've often thought about somehow hooking the electric pump back up to a switch to use to prime the carb, then turn it off before starting the Bronco.

If you go this route, use it to prime the carb, not the mechanical pump as jckkys suggests.

 

[Broncobowsher]

The biggest issue I see is the electric pump is normally a huge restriction to flow if it isn't running.

The mechanical pump uses a spring on the diaphragm to create the pressure. The pump arm compressed the spring and pulls the diaphragm back for a suction. Pushing fuel into a mechanical pump won't bother it or change output pressure so long as the electric pump isn't running a higher pressure.

 

[Brax601]

Thanks for the feedback everyone. It seems like the issue of the bowl being dry after sitting for a little while is what I’m having happen. Sometimes it does seem to be slow to start after shutting down. I wonder if this has to do with the vapor lock that you mentioned Rustytruck.

 

[Rustytruck]

Bronco carbs run hot, fan blows hot air right at them so fuel is pretty much dried up in a few days especially with the added alcohol. so the crank, crank, crank issue. When i park my truck for long periods i use a small squeeze bottle filled with gas and squirt it down the carb vent the night before to fill up the fuel bowl when I want to start it up. Starts like normal the next morning. my issue is a little different as I run a Quadrajet carb. it has no hot restart issues. so no hot restart vapor lock problems. its fuel bowl is less than half the size of the fords and sitting in the center of the venturies instead of hanging out in the direct heat. when Quadrajets dry out the leather pump on the accelerator needs to swell back up to be functional. fords motor craft doesnt have those issued it just needs a full fuel bowl.

 

[jckkys]

The fuel bowl filling electric pump does create an obstruction for the mechanical pump to pull through. Actually the atmospheric pressure pushes the fuel, but the effect of an obstruction is the same. A parallel fuel line circumventing the electric pump and containing a one way valve may be less of an obstruction. I don't know. Some electric pumps are called pull through. I don't know how easy that is in terms of absolute pressure drop. Ending the dry fuel bowl problem may create a vapor lock problem. My solution is to drive the EB more often.

 

[Ovalis]

My broncos aren't daily drivers so I always have the issue of fuel bowls evaporating.
I try to get out there and start them and let them run for 30 seconds to fill up the bowl, but there's a lot of times that I forget so I keep some gas in a squirt bottle to manually fill them up. When I'm out of gas, my back up is a can of starter fluid and that will let the engine run long enough for the pump to fill up the bowls.

 

[Broncobowsher]

My last carbed V8 I would keep a squeeze bottle of 2-stroke premix handy. Little squirt down one of the vacuum ports that was handy to access. 2-stroke mix to add a little lube to minimize the gas wash of the cylinder walls. And because the only gas can I keep anything in happens to be premix.

 

[jckkys]

It would be nice to be able to fill a dried out float bowl from the driver's seat. The Ford carbs are less problematic than some other carbs the Q-jets and AFBs have leather accelerator pumps. Holleys have bowl gaskets that dry out and crack or wrinkle up causing leaks. I hate to keep a bottle of gas in the truck to fill the float bowls. Some experiments are in order. For those living in wet climates this may not be as much a problem. When I lived in the Chicago area I never had this problem. Summer in Tucson can dry out the float bowl in 2 days. On the other hand there's no rust.