Fuel Pump vs Electric Pump

[grewvin1]

1987, 5.7L merc. V8, 4bbl. Question is after week of no use take a few cranks and pumps of throttle to get going normal for carb. engine. Would changing to an electric fuel pump allowing it to pump up when ign. on put fuel into carb faster than mech. pump and diaphragm ?

 

[Bondo]

Ayuh,.... A properly wired up electric fuel pump, don't see any power, til the motor is crankin' on the starter, or there's oil pressure in the motor,...

So,... Nope, it won't necessarily start quicker, unless ya hot-wire the pump,.....

A better answer is to just rebuild the carb, so it don't leak off anymore,...

 

[grewvin1]

thanks

 

[wrench 3]

If you're running a Rochester Quadrajet carb, that is a common problem with them. Rebuilding or replacing the carb will probably have little affect. Usually the extended cranking time is more of a nuisance than a problem.
If you're serious about fixing it you could "properly" wire in an electric pump and add a momentary contact primer switch.

 

[batman99]

If installing an electric fuel pump instead of using factory mechanical fuel pump, recommend wiring in the electric fuel pump the safe way.

Method 1 (IMO - unsafe) - which some folks do.
- connect the fuel pump "+" wire to the run side of ignition key. Depending on wire thickness, may need to install a relay as well. When key is in ON position, the pump is running. Clean / simple but IMO, very unsafe.

Method 2 (IMO - proper way)
- Also install a oil pressure switch and connect to fuel pump's upstream relay. . When engine is turning over, the fuel pump is active. If engine has NO internal oil pressure (assume engine has 0 RPMs), then fuel pump is OFF - regardless of ignition key position. This is a safety feature also mandatory in racing engines.

Wire diagram: http://www.allfordmustangs.com/forum...ng-diagram.jpg

Either wiring method will work. But if I was installing an electric fuel pump in my boat, I'd use method 2 (which is used on vehicles as well).

And to stop fuel pump from over pumping fuel, do confirm if your specific brand/model of electric fuel pump also needs an inline regulator as well. Another safety that some makes/models of fuel pumps need.

Hope this helps.

 

[bruceb58]

Method 2 (IMO - proper way)
- Also install a oil pressure switch and connect to fuel pump's upstream relay. . When engine is turning over, the fuel pump is active. If engine has NO internal oil pressure (assume engine has 0 RPMs), then fuel pump is OFF - regardless of ignition key position. This is a safety feature also mandatory in racing engines.

You also need to add a connection that allows the pump to be on while the engine is cranking since there is no oil pressure until you crank for awhile. This is actually shown on your diagram

 

[batman99]

You also need to add a connection that allows the pump to be on while the engine is cranking since there is no oil pressure until you crank for awhile. This is actually shown on your diagram

Yes. More details are within the diagram. re: Drill down URL.

 

[thumpar]

When you push the throttle after it has been sitting do you get a squirt of fuel from the carb? If not your fuel bowl is not staying full.

 

[wrench 3]

When you push the throttle after it has been sitting do you get a squirt of fuel from the carb? If not your fuel bowl is not staying full.

That is exactly the problem with the quadrajet carb. The fuel bowl fills from the bottom rather than the top like most carbs. Once enough fuel has evaporated for the float valve to open, most of the remaining fuel drains back into the fuel tank.

 

[NHGuy]

Qjets do not fill from the bottom. They fill from the side. They are exposed to atmosphere by their vents so the fuel level drops during periods when not in use. From evaporation.
No need to over think things.
To start up. Run your blower. Pump the throttle maybe twice or thrice. Crank for a few revs. If nothing happens stop the crank, pump it a couple times & crank again.
It ain't fuel injection. You gotta get fuel into the bowl so the engine can suck it past the venturis. If you ever really want to prove that to yourself just drop a little gas down the primary bore sometime and then crank. The motor will light off on the first or second compression cycle.

 

[NHGuy]

Once you have started it, it will start on little or no pumps of the gas for that day. And the next day you'll be able to start it with 1 or 2 pumps and a crank. But after two or three days not used the fuel bowl will have lost some gas.

 

[Fed]

Move the throttle up to wot once to set the auto choke then pump while cranking over. You should hear the choke make a plink sound when it sets.

 

[achris]

Move the throttle up to wot once to set the auto choke then pump while cranking over. You should hear the choke make a plink sound when it sets.

To 'set the auto-choke' you only need to lift the throttle off the idle stop. No need to go to WOT. Going to WOT will assist in getting a squirt of fuel through the accelerator pump, if there's fuel in the carburettor.

Chris.

 

[Fed]

Maybe mine needed adjustment chris, it's been a long time but I'm sure I had to move a fair way off idle to get it to engage.
Probably old timers setting in, have a happy australia day mate.

 

[wrench 3]

Qjets do not fill from the bottom. They fill from the side. They are exposed to atmosphere by their vents so the fuel level drops during periods when not in use. From evaporation.
No need to over think things.
To start up. Run your blower. Pump the throttle maybe twice or thrice. Crank for a few revs. If nothing happens stop the crank, pump it a couple times & crank again.
It ain't fuel injection. You gotta get fuel into the bowl so the engine can suck it past the venturis. If you ever really want to prove that to yourself just drop a little gas down the primary bore sometime and then crank. The motor will light off on the first or second compression cycle.

Hay, I tend to over thing everything. Drives the wife crazy.
I was going with the drain back theory because the float valve screws into the bottom of the float bowl. Not into the air horn like most. But there might be merit to your evaporation theory. They do have a smaller float chamber than most.
If mine has been sitting for a week, no amount of pumping will have an affect until it's been cranked for about five seconds to bring up some fuel. Five seconds doesn't sound like much, But it feels like forever when your leaning on the key.