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While half way watching the super bowl, and chasing down wiring in the schematic I down loaded from our site. I am pondering why? is there an electric fuel pump on my 1950 Super deluxe I purchased last year?. Is there some huge advantage over a manual type of fuel pump?. Why do a lot of people do this?. As I am checking and rewiring this car,I find no fuse to the fuel pump. To me this is very bad. I'm just looking for opinion's, and your thoughts. Because I am perplexed and am looking for opinions.

Dave O

This is one of those no matter what you do issues. Some will be for it and some against or see no need. I am on the it cannot hurt side as are many of us who have added an electric pump near the tank controlled by a switch under the dash. It should definitely be fused and as I recall, the mfg of my pump suggested a 10 amp fuse.

A solenoid or pulse type electric pump will allow the mechanical pump to pull fuel thru when turned off. Rotaries are quieter and can be used but generally will not allow fuel to be pulled thru when off so require extra plumbing and check valve to route fuel around the pump when it is off.

Usual procedure is to turn on the pump for awhile before trying to start the car after it has sat for a few days. With todays fuel so volatile many have had issues with it "boiling off" after the engine is hot and then turned off for several hours or particularly after the car sits for a few days. By running the pump for a period of time the fuel is pushed up thru the regular pump and filters into the carb to fill the bowl so the engine does not need to crank such a long time in order to bring fuel and fill the carb. Once the engine has started the pump can be turned off and mechanical pump does the job as designed. As long as the mechanical pump is kept in good condition there is no downside but you do need to make sure the mechanical pump has a good diaphragm or fuel can go into the engine.

Another time it might be used is in the case of vapor lock. Again, volatile fuel can form bubbles on the low pressure or suction side and if one of those bubbles is large enough and lands just right in the mechanical pump the mechanical will lose suction and result in what is commonly referred to as vapor lock. Turning the pump on when the first symptom occurs puts pressurized fuel on the low side and also pushes fuel thru so bubbles are no longer an issue.

Howard, Thanks!. I knew you'd help me out first!. So now putting a side the shrimp dip and hot sticks, I don't want to know the outcome of the game as you are a hour ahead of me. I can see what your talking about. My question now is, can the mechanical pump pull through the electrical pump? or is some re- piping needed?.

Dave

OK Howard, putting the Super Bowl rum and coke aside. I re read your e-mail, and you did cover my last question in your e-mail. On how it could pull fuel through. My question now is should i put a fuel pressure meter/gauge before the carb?. As currently I don't know what pressure the electric fuel pump is putting into the carb.

Dave O

PS I now know the outcome of the Super Bowl.

The solenoid or pulse pump has two valves very similar in operation to those in the mechanical pump. When the pump is operating the solenoid works a kind of diaphragm arrangement and valves are functional. If it is turned off the mechanical pump suction will just pull the valves open and fuel can flow thru the pump.

The rotary pump has a set of offset gears similar to an oil pump or some tightly fitting vanes mounted on the motor shaft which rotate in a chamber. As those turn the fuel is pulled in from one side, pushed thru the spaces between teeth in the gears or vanes in the chamber and expelled out the other side and on to the engine. Once the pump stops the gear or vane segments form a fairly tight seal so any fuel is blocked from passing thru the pump.

In order to use a rotary it usually needs a parallel path for fuel to flow. That path has a check valve in the middle. If pump is running it prevents the pressurized fuel out of the pump from flowing backwards and into the pump inlet side again. When the pump is off then the suction of the mechanical pump opens the check valve and allows fuel to flow thru that path.

Here’s my setup. Fuel pump, adjustable gauge set to 4 or 5 lbs, check valve on the bypass line.

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Part of the issue has been very poor quality mechanical pumps being sold lately. I went through 4 in a few months for the Cad after rebuild and finally opted to go all electric. They moved production and I wrote the company several times but no change/refunds. Better to rebuild what you got. I rebuilt the '49 P dual pump & carb and had no issues after.
I guess you need to decide if you want electric pump in or out and plan accordingly with your wiring.(and if doing 6 or 12 VDC)
I don't like the "booster" or "primer" toggle switch approach because you may leave it on and flood the carb. Most electrics deliver way too much pressure and flow for carbs. What they're made for, FI, is usually on a loop so it don't matter. But the carb float needle valve is not held very tight. It's a simpler install this way but still needs a fuse and a momentary switch(my opinion) so you don't forget to shut it off.
You can find a diagram for making them "foolproof" online but requires a different oil pressure switch and some relays, etc. I think Airtex has a pump that delivers the correct pressure for carbs without external regulator, but as I found it's rather noisy. (not sure if 6V available) Most require a pre-filter so maintenance and placement issue.
I put fuel pressure gauges in my carbed vehicles.

I used three position on off and momentary switch in my system. Also carry piece of robber tubing in event either pump becomes inoperable. Future plan on installing light in circuit to remind me of operation of electric pump

Thank you all for your opinions, they are much appreciated. I have decided to fuse the pump, put in an oil pressure safety switch, and an adjustable pressure regulator with gauge, and leave well enough alone, since it was working just fine the way it is.

Thanks again
Dave O