Technical Can i leave mechanical fuel pump on engine when installing electric one ?

53 Victoria, stock 239 flathead two 2 barrel carbs. Going to install an electric fuel pump and was told by a friend who's a retired mechanic that it is not necessary to remove the mechanical fuel pump. He believes it will run fine with both operating.

What do you guys have to say about this ?

thanks-

 

Not sure about a flattie with 2 two bbl carbs,but I did it with a stock 390 in a 63 T/bird and has done a zillion miles like that with no probs.My reasoning was that while the car sat from weekend to weekend,the electro pump just helped to get fuel up to the carb easier than just cranking the engine etc.Not really traditional but does save the battery and starter. Hope this helps

 

I would remove it and put a cover plate on. Makes no sense to me to run 2.

 

If the pump diaphragm starts leaking fuel into the crank case, you might have problems...but if the pump is in good condition, it should be fine.

 

That is the way my Motorhome is. The fuel tank is so far away from the engine that the stock BB Chevy fuel pump can't pull it far enough so it has an electric back by the tank. The only thing I am afraid of is if the mechanical springs a leak fuel will go everywhere.
I'll be interested in what everybody else says.

 

The flathead mechanical fuel pump location made it especially prone to vapor lock, so the addition of a electric pump back at the tank was very common back in the day. With quality and range of electrical pumps available today I'd just run the electric pump w/ a filter and regulator inline

 

You could put a switch on the electric and only run it for starting or if you get vapor lock. That is what a lot of guys do.

With both operating you might want a pressure regulator for the carbs.

 

I had a electric inline on my old Pontiac and it was on a switch. the motor ran with the mechanical one all the time. then one day while driving my mechanical one started to fail and I flipped the switch on the electric pump and the car drove fine until I replaced the mechanical one. so yeah..run both if u want to

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Wondering as to your reason for installing the electric pump on the Vicki.
I have my mechanical plus the electric, on a toggle, on my dual carb, 235..
I use the electric to fill the bowls on the carbs, eliminating the ongoing crank, crank, crank to fill the bowls ... with only the mechanical pump..
Once the electric fills the bowls, the starter button is pushed, engine fires up immediately, the electric pump is shut off.
A good back up, as well, if the mechanical takes a dump, on the road.

 

My flathead 6 came with both, never had any problems.


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I have an electric pump on my flathead '40 for priming and backup. Never had a problem.

 

I thought the answers would have gone the other way. Do you split the line or go through the mechanical one?

 

Go thru the mechanical one. It has 2 one way valves, the pressure will just push thru.

The only danger, besides too much pressure, is that if the mechanical pumps diaphragm ruptures you can get gas in the crankcase. But, this rarely happens with any fuel pump failure.

 

I don't want to hijack this thread but does anyone know if the electric Carter fuel pump will flow through when you shut off power? I was thinking of putting a mechanical pump on with my Carter electric and wondering if it would pull through the Carter if I killed electric power to it.

 

You can leave it in place, but remove the fuel lines.
A cracked/ruptured/broken diaphram will end up dumping fresh fuel into the oil pan..! Unless you like that idea...!?

There is NO good or safe reason for leaving the mechanical pump in the fuel system after adding an elect. pump.
Many "may" have gotten away with this practice...but I'd just bet that the ones who haven't gotten away with it... you'll NEVER hear from them because they don't want to be ragged on by everyone..!

Just plain and simple...a BAD practice.

Mike

 

Rotor Carters will not flow through when off. Only the push pull ones will.

You would have to route a bypass with a check valve.

 

Thanks.

 

Do you mean with both hooked up or?

Back in the '60s we used to do it with both hooked up to eliminate fuel surge. But without the mechanical hooked up works as well, it works as a block off plate.

Anyway maybe you should clarify what you are wanting to do.

 

had several collector cars that I did that with, because they sat for long periods of time between running, had a small toggle switch for the electric fuel pump. would turn on the pump , give it a minute to prim the carb and once the car was running would turn it off and run of the mech. pump, would save a lot of cranking and batt. trying to pump the fuel and prim the carb on a car that sat for months some times

 

I had quite a few 6 volt flathead cars with the stock pump, added a 6 volt 'Autopulse' electric pump on my '36 (next to the tank) and could toggle it off when running.
I was an auto mechanic, so maintenance was performed religiously.
Worked fine, so...never say 'NEVER!'
If the mechanical fuel pump diaphragm fails, it is usually due to an old or third rate pump.
Most fuel pump diaphragm failure sucks oil, emitting a smoke screen from exhaust. Otherwise, occasional checking of the dipstick may indicate the presence of gasoline in the oil...it can also be detected by its odor...

 

Mike good info. One would not want to run a positive pump like say a Mallory or Holly vein pump in front of a mechanical pump. It would override the pump at least and maybe even flood your crankcase.

Anyway I should have clarified and you did just that thanks.

 

One other thing to consider, is there anything under the hood/dash that pulls vacuum off the fuel pump? ( Wipers, Power brake booster, etc. ) Someone posted last week that they'd gone to an electric pump, and suddenly a bunch of stuff wasn't working. So regardless of if you route the fuel around the old mech. pump, or through it with a new diaphragm, there may be a reason to leave the old pump in place.

Kinky6

 

Yes....BUT a friend just had big probs on his Olds powered boat until he bypassed the mechanical pump. Confused us both

 

Electric with a block off plate.
If its looks your worried about, run dummy lines so any rube will think youre still mechanical.

 

I have one of each. The coupe has just an electric & the roadster has an electric on a dash toggle & a mechanical. The mechanical pulls thru the elec when off with no problem.

 

As a primer i see no issues. If your mech stops working there is a reason and pumping gas through it is probably not real good. If you want the look of the pump then make a dummy mech pump and run the electric.

I can leave a 6v mech fuel step up for weeks. Couple pumps of the spoon, little choke, and a few cranks it fires right up. I would say its due to non eth fuel, a good carb that keeps fuel in the bowl, tested fuel pump, and luck. A decent coil and condenser isn't a bad thing either.

Had issues with a vapor lock issue but it turned out to be a coil issue.

 

Common practice in drag racing stock type cars run both. Look at the junior stock photos and you will see many set up and running both at the same time.

 

Guys thanks for all the replies to my question. To answer a couple questions-

Reason for going to the electric pump is because the mechanical one isn't getting the job done, not putting enough fuel into the carb. We replaced the steel rod in the fuel pump when motor was rebuilt about 4 years ago & cars had few miles put on it since then.

We are interested in leaving both pumps hooked up & functioning. After reading all the posts I like the idea of a toggle switch, using the electric pump to prim the carbs, then shutting it off. We'd have to figure out why the mechanical pump isn't providing enough fuel though.

One of you wrote "Rotor Carters will not flow through when off. Only the push pull ones will." We bought a Carter P60504. Will the mechanical pump pull thru this Carter if the electric pump is off ? I'm not familiar with rotor pumps.

thanks again-

 

http://forums.aaca.org/f120/electric-fuel-pump-priming-only-308137.html

post12

 

Have you put a fuel pressure tester on it to see what it's pumping? Also depending on what 2x2 barrel intake you might need a different length fuel push rod. I believe the offy needs either a longer or shorter (I forget) rod.

Could be a number of reasons the pump isn't preforming as well as it should though.