1951 Merc elec fuel pump

hoffernsp

hoffernsp

Member
Here is a pic of the electric fuel pump that was on the 51 Merc when I bought it.
Why was it installed on the fire wall above the carb? Don't they normally push not pull and should be low near the tank? Would it still work where it's at? The car ran when I got it 2 years ago.
Any thoughts/suggestions?
 

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You are correct in that the design of the pumps makes them better pushers than pullers. Most installations are done at or very near the fuel tank so they can push. A diaphragm type pump is generally used to pull fuel any distance since it has less tendency to cavitate.
 
The best location for an electric fuel pump is as low and close to the fuel tank as practical. They will work in other locations, but at decreasing efficiency the higher and further the fuel has to be pulled vs pushed.
 
JSeery said:
The best location for an electric fuel pump is as low and close to the fuel tank as practical. They will work in other locations, but at decreasing efficiency the higher and further the fuel has to be pulled vs pushed.
Click to expand...

Any guess as to why it was installed where it's at?
 
That looks to be a pic of a rotory vane pump and I have found that they work just as well as the original pump regardless of location.
Just about all the pumps now are solid state Facet type pumps and have a limited lift capacity that requires that they be mounted in a low place, immersed in fuel in order to keep a 'prime'.
 
Be sure to replace those "spring clamps" with better hose clamps.
Also, replace the fuel hoses with alcohol resistant hoses.
Is there any brand name or part # on the pump?

Oh, be sure to insert your wiring in those clips that run
along inside of cowl as seen in your photo.
 
36rgtop said:
Really?:confused:
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Yep, what is the question? Fuel (or any liquid for that matter) doesn't work well being pulled by a vacuum. Different liquids have a different height/distance that they can be pulled before the liquid transitions to the gas phase. Gasoline can not be pulled very high or over much distance and as the heat increases that become less and less. This has nothing to do with electric pumps, it is not the pump, it is the lowered pressure created to pull the fuel. There are different factors that make some pumps work better in one locating vs another.
 
Leave pump alone and drive it to see how it runs. If it works fine, you are good to go. Keep an extra pump in the trunk as a spare.
 
19Fordy said:
Be sure to replace those "spring clamps" with better hose clamps.
Also, replace the fuel hoses with alcohol resistant hoses.
Is there any brand name or part # on the pump?

Oh, be sure to insert your wiring in those clips that run
along inside of cowl as seen in your photo.
Click to expand...

No nothing on the pump body at all.
 
Diaphragm type pumps pull a better low pressure draw than piston, gear, gerotor, or rotary vane types but some of them will work better than others depending on design. The diaphragm types have no way for fluid to pass through or around gaps since there are none. The others all have a certain amount of leakage past their wear points and gaps. Air in the system is also a factor since air passes through leak points much easier than fluid does since a gas compresses. Once a pump is primed it's good to go but cavitation can happen if it has lost its prime.
 
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It should be installed as close to the tank as possible with a filter located between the tank and the pump. The closer it is to the tank the easier it will be for the pump to prime. Where its mounted now the fuel can drain back into the tank. Each time you turn the pump on it has to remove all that air out of the line. Mounted down low where the fuel level in the tank is the same level as the pump the hose between the pump and tank will stay primed with fuel. A check valve located in the pump should prevent the fuel between the pump and carburetor from draining back down into the tank. Obviously its working where its located but its not correct.
 
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