Mechanical Fuel Pump question
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Elder User
Joined: Feb 2019
Posts: 548
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From: NC
Mechanical Fuel Pump question
Everything on my 64 223 is brand new, including all new lines, pump, and fuel tank, so all fuel lines were completely dry starting out. I cranked for a bit for the first time ever today and couldnt get fuel to the filter. I eventually disconnected it from the line, and ran a hose into the gas can, and it primed really quick maintaining the filter at about 3/4 full, so pump is definitely good.
I then unhooked it from the gas can and hooked it back up to the main line, started it again. It ran, and will continue to run currently, but theres definitely something I'm not doing properly it seems.
As can be seen in the pic, that is as full as the filter will remain now, but it happens to be enough to keep it running. The fuel is coming into the filter in short little bursts followed by short pauses.
Do I just need to keep running it and it will work itself out? Or am I skipping some important priming step that I dont know about?
Fleet Owner
Joined: Jan 2004
Posts: 26,007
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From: Brentwood,CA
Is that in line filter on the suction side? Hopefully so because you don't want a plastic filter especially with friction clamps on the pressure side. The fuel flow you describe is normal, fuel is only going to flow enough to fill the bowl. There isn't a constant stream of fuel like you would find in a system with a return.
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Elder User
Joined: Feb 2019
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From: NC
Is that in line filter on the suction side? Hopefully so because you don't want a plastic filter especially with friction clamps on the pressure side. The fuel flow you describe is normal, fuel is only going to flow enough to fill the bowl. There isn't a constant stream of fuel like you would find in a system with a return.
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Elder User
Joined: Feb 2019
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From: NC
Thats what I have. It appears that it is, but not sure. Initially after switching from the gas can to hooking back up to the fuel tank, the filter was half full. At one point, I took of the gas cap and blew in there to try to force some fuel in (read that in another post on this forum when searching). Once I pulled my mouth away, I got hit with a gush of air from the tank, and at that point, fuel level in the filter dropped to where it's at now.
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Elder User
Joined: Feb 2019
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From: NC
I would think it should be atleast half full though, right? When I ran a 1 foot hose off the the filter to a gas can initially, it maintained about 3/4 full, which is what i would have expected.
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Thread Starter
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Elder User
Joined: Feb 2019
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From: NC
Main thing I was wondering about was whether I would damage the pump by running it for long periods without the proper amount of fuel being fed to it.
Post Fiend
Joined: Apr 2002
Posts: 19,311
Likes: 97
From: Waterloo, Iowa
The smallest air leak in system the pump will have trouble. Pump needs to supply both adequate pressure and volume. For volume test just direct a hose from the fuel pump outlet into a clean container and idle the engine. It should pump at least a pint in under 30 seconds. A mechanic's vacuum gauge also measures fuel pump pressure. 5 to 6 psi is plenty.
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Elder User
Joined: Feb 2019
Posts: 548
Likes: 1
From: NC
The smallest air leak in system the pump will have trouble. Pump needs to supply both adequate pressure and volume. For volume test just direct a hose from the fuel pump outlet into a clean container and idle the engine. It should pump at least a pint in under 30 seconds. A mechanic's vacuum gauge also measures fuel pump pressure. 5 to 6 psi is plenty.
Was able to tighten that up, turned her over, and fuel filter immediately returned to being 3/4 full. Good to go now!
Post Fiend
Joined: Apr 2002
Posts: 19,311
Likes: 97
From: Waterloo, Iowa
Good deal. Old fuel hose can also leak a bit past the line where it connects. It doesn't take much.
Many new fuel pumps are suspect these days just as a FYI .... installed a new pump a year or so ago and had to crank the float down lower and lower .... till it was practically at the bottom of the bowl. That isn't right. Should have measured it from the gitgo, could have got my money back. 8.5 psi, almost double the factory spec. It gouged the fuel inlet needle tip pretty good, it would have flooded sooner rather than later I think. Just sayin', just because parts are brand new doesn't mean much anymore.
Many new fuel pumps are suspect these days just as a FYI .... installed a new pump a year or so ago and had to crank the float down lower and lower .... till it was practically at the bottom of the bowl. That isn't right. Should have measured it from the gitgo, could have got my money back. 8.5 psi, almost double the factory spec. It gouged the fuel inlet needle tip pretty good, it would have flooded sooner rather than later I think. Just sayin', just because parts are brand new doesn't mean much anymore.
Thread Starter
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Elder User
Joined: Feb 2019
Posts: 548
Likes: 1
From: NC
Good deal. Old fuel hose can also leak a bit past the line where it connects. It doesn't take much.
Many new fuel pumps are suspect these days just as a FYI .... installed a new pump a year or so ago and had to crank the float down lower and lower .... till it was practically at the bottom of the bowl. That isn't right. Should have measured it from the gitgo, could have got my money back. 8.5 psi, almost double the factory spec. It gouged the fuel inlet needle tip pretty good, it would have flooded sooner rather than later I think. Just sayin', just because parts are brand new doesn't mean much anymore.
Many new fuel pumps are suspect these days just as a FYI .... installed a new pump a year or so ago and had to crank the float down lower and lower .... till it was practically at the bottom of the bowl. That isn't right. Should have measured it from the gitgo, could have got my money back. 8.5 psi, almost double the factory spec. It gouged the fuel inlet needle tip pretty good, it would have flooded sooner rather than later I think. Just sayin', just because parts are brand new doesn't mean much anymore.
I was really surprised how quick she cranked and how perfect it ran off the get go, despite the fuel sucking some air in. If I could post a video of the first crank ever my me, I would but dont know how. Literally 2 second crank, fired right up and idled smooth. And when I rebuilt the carb, I just randomly put the air mixture and idle screws back in place and lucked out with where I set em at. I'm sure it could use some minor tweaks, but nothing to stress over
Cargo Master
Joined: Jan 2016
Posts: 2,671
Likes: 372
It will never fill due to the way you primed the fuel line (by sucking) regardless of how airtight the line to the tank is.
If you want the filter to be full, you'll have to prime the line by pushing fuel while holding the filter upright. It can be done with some creativity. One way is to apply about 5 psi to the fuel tank until fuel pushes through the filter. You'll want to disconnect the fuel line just before the pump and then reconnect it after the fuel fills the filter. This way you can fire the engine with minimal cranking...especially important if breaking in a new camshaft.
If you want the filter to be full, you'll have to prime the line by pushing fuel while holding the filter upright. It can be done with some creativity. One way is to apply about 5 psi to the fuel tank until fuel pushes through the filter. You'll want to disconnect the fuel line just before the pump and then reconnect it after the fuel fills the filter. This way you can fire the engine with minimal cranking...especially important if breaking in a new camshaft.
Thread Starter
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Elder User
Joined: Feb 2019
Posts: 548
Likes: 1
From: NC
It will never fill due to the way you primed the fuel line (by sucking) regardless of how airtight the line to the tank is.
If you want the filter to be full, you'll have to prime the line by pushing fuel while holding the filter upright. It can be done with some creativity. One way is to apply about 5 psi to the fuel tank until fuel pushes through the filter. This way you can fire the engine with minimal cranking...especially important if breaking in a new camshaft.
If you want the filter to be full, you'll have to prime the line by pushing fuel while holding the filter upright. It can be done with some creativity. One way is to apply about 5 psi to the fuel tank until fuel pushes through the filter. This way you can fire the engine with minimal cranking...especially important if breaking in a new camshaft.
As for now, I'm happy with where shes at. She runs great, and after tightening my tank pickup line, I have the filter filled to the same level coming from the tank now as I originally had it coming straight out a gas can.