Mechanical versus electric fuel pump

Wayne Maybury · #1 (**permalink**) 05-20-2009, 06:53 AM

I have a mechanical fuel pump that works perfectly but I do have to crank the engine quite a bit to pump gas up to the Holley if the car has been sitting for a few weeks. I know, drive the car more but that is not always possible due to business travel and/or the weather. An electric pump would fill the carb instantly without cranking the engine. I have been thinking about adding an electric pump rather than just converting to one. Has anyone done this? Will both pumps function properly in the same gas line, one ahead of the other or should I just go to an electric pump? Any drawbacks to this plan?

Wayne

Bill Bess · #2 (**permalink**) 05-20-2009, 07:04 AM

The mechanical pump will not let you down...if it does most parts stores carry one and it's an easy fix. Electric only can be tricky to find..maybe carry an extra, maybe difficult to change?
Using an additional electric pump will work just fine, maybe put a switch on it and use it to prime the carb or run it all the time..your call.

Bill

cdnus · #3 (**permalink**) 05-20-2009, 07:22 AM

Wayne
After just a few weeks of sitting you should be able to pump the peddle a few times & have the engine fire up on gas remaining in the carb.
By continuing to pump the peddle after firing you should be able to keep it running.
If you have to crank for a long period of time (read-run the battery low) it may indicate you have a small air leak between the tank & pump.
Easy to check--dis-connect the fuel line from the carb & close it off with the appropriate fitting. Then dis-connect the fuel line comming out of the tank & with the required fittings attach a air line quick connect.
Now connect a low pressure--5-10 lbs to the line & you will know almost instantly if you have a leak any where in the system.
The whole procedure only takes 1/2hr. & quickly eliminates any question in the system.

Craig

P.S.
Didn't include the usual warnings about working with gas etc. You know all that Right?

jwd · #4 (**permalink**) 05-20-2009, 07:33 AM

It's very common for the carb. to be dry after sitting for several weeks. Since it is vented to atmosphere and the carb. and engine are very hot when it's shut off, the fuel evaporates quickly. I like the fact that I have to crank it a bit after sitting because that builds the oil pressure before it fires up. Keep the mechanical pump.

Jim

jhv48 · #5 (**permalink**) 05-20-2009, 07:44 AM

Maybe a dumb question, but will having an electric fuel pump between the tank and the mechanical fuel pump bypass the mechanical fuel pump and fill the bowls? Or will it just build up pressure between the tank and the mechanical fuel pump?

Thus accomplishing nothing!

priobe · #6 (**permalink**) 05-20-2009, 07:59 AM

If you are determined to keep the mechanical pump, I would install an electric pump with a check valve at the electric pump side and install a relay with a timer circuit for 5 sec.

Every time you turn the key the electric pump will cycle for 5 sec priming the fuel bowl. If you really wanna get trick install a temp switch that will only allow contact at 120 degrees or below. This will only allow the pump to run only when the motor is dead cold.

It seems like a alot or complicated but it really is not. Besides you can always stay with your mechanical as others have mentioned but where is the fun in that

What ever your choice we are here for you.

ERA Chas · #7 (**permalink**) 05-20-2009, 08:09 AM

Wayne,
This was all covered in a knock-down-drag-out thread a couple weeks ago here:
Fuel Pumps - Electric vs. Mechanical

You can draw your own conclusions.

Wayne Maybury · #8 (**permalink**) 05-20-2009, 08:31 AM

Quote:

Originally Posted by ERA Chas

Wayne,
This was all covered in a knock-down-drag-out thread a couple weeks ago here:
Fuel Pumps - Electric vs. Mechanical

You can draw your own conclusions.

Thanks for the feedback. I missed that thread but I will go through all 3 pages a little later today.

Who would have thought that mechanical versus electric fuel pumps could stir up so much emotion? It is almost like the big block versus small block issue.

cdnus; Actually the fuel in my float bowls evaporates within a couple of weeks. I have spoken to a few hot rodders who say this is quite normal. I have checked and I do not have any leaks. I do not have an issue with the fuel pump or gas line, just the fuel in the bowls.

Wayne

ERA Chas · #9 (**permalink**) 05-20-2009, 08:43 AM

Wayne,
It's quite normal to have that rate of evaporation. I'm one of the few that runs an electric feeding a mechanical. I outlined my reasons and experience in the thread.

jhv48 · #10 (**permalink**) 05-20-2009, 09:48 AM

As part of your pre-drive routine after the car has been sitting for a few weeks, you could always use a squeeze bottle and pour gas directly through the bowl vents to partially fill the bowls so the car lights right up.

Wayne Maybury · #11 (**permalink**) 05-21-2009, 07:01 AM

Quote:

Originally Posted by ERA Chas

Wayne,
This was all covered in a knock-down-drag-out thread a couple weeks ago here:
Fuel Pumps - Electric vs. Mechanical

You can draw your own conclusions.

I read that whole thread and I guess that I will stick with my mechanical pump. The cranking porblem only occurs when I first start the engine in the spring or when the car sits for several weeks. I can live with that and I do like to keep things simple. Adding an electric pump would just be a step towards complexity.

Wayne

Snakebit · #12 (**permalink**) 05-21-2009, 02:45 PM

I just had a carter mechanical pump crap out on me after 300 miles! Was able to nurse it home. Would have had to call a tow truck if it was electrical. A friend of mine who is a farmer and trucks his crops to Philly had an old ford box truck. The mechanical pump died so he replaced with an electric pump. The fuel pump dies on the Walt Whitman bridge. $1000.00 to tow the truck off the bridge!!! He took that electric pump and threw it as far as he could.
If you are running fuel injection, electric pumps have their place, and like they said, they are mounted in the tank. If you are running carbs, stick with the mechanical pump.

ERA Chas · #13 (**permalink**) 05-21-2009, 04:04 PM

Quote:

Originally Posted by Wayne Maybury

I read that whole thread and I guess that I will stick with my mechanical pump. The cranking porblem only occurs when I first start the engine in the spring or when the car sits for several weeks. I can live with that and I do like to keep things simple. Adding an electric pump would just be a step towards complexity.

Wayne

Wayne,
I hear and respect your opinion.
I just want to say that this system has been on my car since 1991 without failure. This also gives you backup in case of one or the others failure. Airliners have triple redundancy so they don't fall down. Now THEY are complex. Cobras are not, they're stone age. (Except Kemmerers car!)
Electric pumps are no where near as complex to install in these cars as the women on here would have you believe. In fact some guys here install twin SW240's or twin Facets just to look correct. A guy who can handle a Cobra can follow instructions and install parts.
Hot or cold, you wouldn't have to crank or WOT with an electric feeding a mechanical. It can make the car a little more enjoyable.

CHANMADD · #14 (**permalink**) 05-21-2009, 04:10 PM

I anyway like the fact that when the cars been sitting I can crank it over and get the oil flowing before I then stop cranking ,pump the gas pedal and then startup!
I do also think that unless you have fuel injection an electric pump is not neccessary and again the mechanical is safer ,as ,as soon as the motor dies so does the flow of fuel........for sure!!
john

Anthony · #15 (**permalink**) 05-21-2009, 05:55 PM

Wayne, from what you have stated, I'd just keep the mechanical. But, if your fuel tank has 2 outlets, like my car, you could run two fuel lines up to the engine, one line to the mechanical, the other to a switch activated, rear mounted electric (keeping this pump mounted as low as possible). Both my lines are -6AN, about 3/8", but -8AN, 1/2" would be better. You could then turn on the electric if drag racing or road racing if your mechanical is not up to snuff, like the way mine is.

If you have only one tank outlet, you could insert a T fitting and do as stated as above, or there are electric fuel pumps that are made to bypass fuel , act as a booster pump when activated, to your mechanical pump, but I'd guess there is some restriction when they are not activated.

I thnk the mechanical in general is more reliable, and choose to run my car this way for street driving or a little spirited driving. But, I need the additional electric for serious engine demands.