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Mechanical fuel pump vacuum

JG1966

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If I hook up a vacuum gauge to inlet port of Edelbrock fuel pump, what amount do I need to see on gauge when I crank motor to know the pump (which is brand new) and more importantly, the cam eccentric is good? About 12? Thanks
 
So I hooked up gauge and turned over with remote starter. Gauge quickly jumped to 20 lbs, then dropped to 0. Couple more revolutions, went to 15 and dropped to 0. Then it started going to about 10 lbs every 5 seconds or so. Does this sound right?

As a backstory, I'm not getting consistent fuel to carb. Float bowls stay empty. Fuel pump is new, fuel filter is new (I got clear one for now to see fuel going in and it stays almost dry). I used a can of gas to cut the tank and fuel lines out of the equation and same thing happened. If I pump pedal I can get a few squirts and it starts but after 10-15 seconds it dies as it runs out of gas. I'm at my wits end. Carb is a fairly new AED Holley 750 DP on a 340. I have pulled carb and the needles are clean.
 
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If the outlet on the fuel pump is closed (float needle and seat closed) I don't think your vacuum will last only a couple of cranks. If the outlet is open then I'd say you got a bad pump. A new one can be bad.

Any leaks from the tank to the pump can cause a loss of vacuum. (Loose clamps, connections, cracks in hoses) A loose connection doesn't always leak gas but will suck air.
 
If the outlet on the fuel pump is closed (float needle and seat closed) I don't think your vacuum will last only a couple of cranks. If the outlet is open then I'd say you got a bad pump. A new one can be bad.

Any leaks from the tank to the pump can cause a loss of vacuum. (Loose clamps, connections, cracks in hoses) A loose connection doesn't always leak gas but will suck air.
Thanks Khrysler. When I used a gas can directly to the fuel pump input, the same things happened, so I think I can rule out any leaks/clogs from tank to pump. The outlet to the pump was open (needle and float open). I'm sure the pump is good. It's brand new and I'm suspecting the pump I replaced it with is still good (that would be way too much of a coincidence). I'm cleaning out carb completely right now and I'm going to replace the rubber hoses at the pump and filter. I'm think the fuel pump eccentric might be worn.
 
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While you're at it.... do you have inlet filters on that carb? (the brass fish tank looking ones). As you said, it "could" also be a worn camshaft fuel pump lobe or the fuel pump "push rod"
 
While you're at it.... do you have inlet filters on that carb? (the brass fish tank looking ones). As you said, it "could" also be a worn camshaft fuel pump lobe or the fuel pump "push rod"

He has a 340. Eccentric could be worn or loose.
 
If you're using regular ol' rubber fuel hose and are running pump gas (with ethanol), that crap will eat the old school rubber lines from the inside - and it'll do it quicker than you think.
I found that out the hard way.
We have to use the fuel line specifically for fuel injection in order for this not to happen.
Yeah, it's $6-$8 a foot, but ya gotta do what ya gotta do.
Just a thought...
 
While you're at it.... do you have inlet filters on that carb? (the brass fish tank looking ones). As you said, it "could" also be a worn camshaft fuel pump lobe or the fuel pump "push rod"
There are no inlet filter on the carb. I just cleaned out carb. It was fairly spotless. Put it back on. No improvement.
 
If you're using regular ol' rubber fuel hose and are running pump gas (with ethanol), that crap will eat the old school rubber lines from the inside - and it'll do it quicker than you think.
I found that out the hard way.
We have to use the fuel line specifically for fuel injection in order for this not to happen.
Yeah, it's $6-$8 a foot, but ya gotta do what ya gotta do.
Just a thought...
I run 5 gallons 110 racing fuel with 15 gallons of 93 octane and always add half bottle of Lucas ethanol fuel conditioner. Hoses seem to be in decent shape. I'm going to put on new ones just in case.
 
I manually filled primary float and she started perfectly and ran fine until the gas was gone. Filter never got more than a half ounce of gas in it. So at least I know carb isn't the problem. Is there any way to test eccentric other than putting on an electric pump or tearing apart front of motor?
 
He has a 340. Eccentric could be worn or loose.
Well, I thought I figured out the problem. I pulled new fuel pump and stuck a screwdriver in hole and cam eccentric is very loose. It rattles if I touch it. I had motor refreshed over the winter so I called the shop and he said all fuel pump eccentrics are loose and should rattle. Is that right?
 
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Well, I thought I figured out the problem. I pulled new fuel pump and stuck a screwdriver in hole and cam eccentric is very loose. It rattles if I touch it. I had motor refreshed over the winter so I called the shop and he said all fuel pump eccentrics are loose and should rattle. Is that right?
@IQ52 ?
and although I'm not having this problem,
I am curious :popcorn:
 
Well, I thought I figured out the problem. I pulled new fuel pump and stuck a screwdriver in hole and cam eccentric is very loose. It rattles if I touch it. I had motor refreshed over the winter so I called the shop and he said all fuel pump eccentrics are loose and should rattle. Is that right?
So there is the answer to the builder's claim that
all fuel pump eccentrics are loose and should rattle.
And could this be the solution in your case?
From FABO linked thread
"Cupped washer towards rear and thrust plate needs to be on. The cupped washer pulls the cam forward against the thrust plate then just line the keyways up and you're good to go."
See pic of correct installation for cupped washer:
Screenshot_20180620-181200_Chrome.jpg
 
So there is the answer to the builder's claim that

And could this be the solution in your case?
From FABO linked thread
"Cupped washer towards rear and thrust plate needs to be on. The cupped washer pulls the cam forward against the thrust plate then just line the keyways up and you're good to go."
See pic of correct installation for cupped washer:
View attachment 618320
They put the washer on upside down!! I'm amazed it ran as long as it did.
20180620_195151.jpg
 
Wow! Thats why I assemble my own engines. Check it for groves and wallowed out opening where the keyway is. If it looks good flip the washer and you should be good to go.
 
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