Fuel pump vacuum lines

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korbin22
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Isuzu vehicle(s): 1992 Isuzu Pickup 2.3L

Fuel pump vacuum lines

Postby korbin22 » Mon Feb 19, 2018 10:05 am

So I’m doing a Weber swap and noticed some things about my fuel pump. One of the vacuum lines was plugged off and the other I might have forgot where it goes :cry: and also the two outlets on the opposite side of the fuel pump on the carb, what plugs into those? I’ll post pictures of what I’m talking about
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korbin22
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Posts: 39
Joined: Wed May 10, 2017 10:22 pm
Location: Jacksonville Florida
Isuzu vehicle(s): 1992 Isuzu Pickup 2.3L

Re: Fuel pump vacuum lines

Postby korbin22 » Mon Feb 19, 2018 10:26 am

Here’s two other pics if it helps tell me where the two fuel line go to. The first picture with the two lines in my hand are the ones I need help with
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oldestisuzuist
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Re: Fuel pump vacuum lines

Postby oldestisuzuist » Mon Feb 19, 2018 12:53 pm

Your fuel pump does not have vacuum lines, only fuel lines. Those two vacuum connections shown in the second picture are for manifold vacuum sources to places that need vacuum, like the distributor, the charcoal canister & the air cleaner.
From the pictures it looks like your pump has four connections, some aftermarket units only have three.
The fuel supply from the tank comes through the top-hat-shaped pulse regulator that's mounted on a separate bracket below the pump. You should feel suction on this line when you cycle the pump arm.
Two of the other connections one is the fuel supply from the pump to the carb & the other is the fuel return to the charcoal canister & eventually to the tank. You should feel pressure/air at both these connections when the pump arm is cycled, the line to the carb is normally bigger and/or the return connection has a restrictor inside it so that more fuel is available to the carb than returns.
The fourth connection- the one that is plugged- is a drain line for the mechanical pump & is absent on some aftermarket pumps. This line should NOT be plugged, the rubber hose just hangs loose down towards the motor mount. Oil or fuel dripping from this drain hose indicates an internal failure of the fuel pump. Replace the pump if either fluid is present, but especially fuel since the fuel can also contaminate the engine oil.
BTW you need two gaskets when replacing the pump, one between the spacer & intake, one between the pump & spacer. Rotate the cam/engine until the pump rod is on the flat/low part of the pump drive cam lobe (#4@TDC), then hold the pump rod up against the cam with a little grease between the retainer clip & head. The pump will then seat all the way without resistance from the pump arm trying to cycle.
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korbin22
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Posts: 39
Joined: Wed May 10, 2017 10:22 pm
Location: Jacksonville Florida
Isuzu vehicle(s): 1992 Isuzu Pickup 2.3L

Re: Fuel pump vacuum lines

Postby korbin22 » Mon Feb 19, 2018 1:09 pm

So where does this fuel line attach to then? I understand all the other ones and where they go but not this one?
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Quahlity
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Isuzu vehicle(s): 1992 Isuzu pickup 2.3 carb

Re: Fuel pump vacuum lines

Postby Quahlity » Sun Feb 25, 2018 12:17 pm

It appears from the picture it goes to the tube that runs up to your carb.
To recap what oldestisuzuist said;

1. from the tank through the fuel filter and through the little pulser to the pump
2. smaller return to the tank.
3. supply to the carb.
4. vent line (it just hangs down)

The vent line is on top of the pump, and not the one you are holding. It doesn't require a clamp, and as shown does not have one. As often as this confuses us all, there should be a special entry in the troubleshooting section.


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