Mechanical Fuel Pump
Thread Starter
Intermediate
Joined: Apr 2014
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Mechanical Fuel Pump
My 68 big block car wasnt getting enough fuel so I installed a new mechanical fuel pump with a new filter.(not easy to get to) It ran great immediately after but when it got hot and i put demand on it, the fuel filter is completely empty and the car runs like crap. I have blown out the line with an air hose back to the tank. And removed the cap while the engine was running but it makes no difference. When you disconnect the fuel line from the pump, gas flows freely all over me! I bypassed the mechanical pump with an electric pump and it pumped worse than the mechanical pump so im not sure it was working properly. with the hose disconnected at the fuel filter it and with the engine running it pumps out gas but not enough to keep the filter full and the bowl in the carb full. anyone know what's going on here?
Last edited by scotish44; Sep 8, 2018 at 09:09 AM.
Le Mans Master
Joined: Aug 2005
Posts: 6,539
Likes: 1,972
From: Temple Terrace Florida
I would look to see if your gas cap is vented. It should be. I would also check the sock in the tank. It is the primary filter. The sock, over time, can fall apart and clog the pickup in the tank. Be careful with the fuel if you have to drop the tank. Jerry
Melting Slicks
Joined: Jan 2000
Posts: 3,326
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From: home
I agree with TJ. Take the cap off and try it. See if it makes a difference. You should be able to see the sock by looking into the fuel filler. DO NOT use an electric light to see inside the tank.
Thread Starter
Intermediate
Joined: Apr 2014
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thanks...the cap is vented and ive taken it off to see if it was a siphon issue, also had it off when i blew the line back from the pump to the tank with an air hose. Gas flow freely out of the line when you take it loose from the fuel pump, so im stumpted.
Thread Starter
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Nothing that can collapse I don't think, it's a metal gas line from that tank to the right before the pump. I put a heat shield around that just in case it was getting hot and vaporizing. the filter inside the tank looks fine, there's particles in the tank but overall it looks good
Team Owner
Joined: Apr 1999
Posts: 21,953
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From: Reno Nevada
2024 C3 of the Year Finalist- Modified
Years ago I bought a Comp cams H-roller 242/248. This is just when the first mush metal cores were being sold and they didn't have a warning about fuel pump rod type. So I was driving down the freeway and my motor started sputtering. So anyway I installed a new ac-delco pump and it did the same thing. I was dumbfounded! 
It turned out that the POS Comp cams mechanical fuel pump lobe went flat and was barely moving the pump rod. I had to replace the cam and from that day on I have only bought billet steel cams and I use the Polymer fuel pump rods from Speedway motors.
I did consider just installing an electric pump instead of changing the cam, but I figured with my big springs the other lobes might go also.
It turned out that the POS Comp cams mechanical fuel pump lobe went flat and was barely moving the pump rod. I had to replace the cam and from that day on I have only bought billet steel cams and I use the Polymer fuel pump rods from Speedway motors.
I did consider just installing an electric pump instead of changing the cam, but I figured with my big springs the other lobes might go also.
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Race Director
Joined: Jul 2004
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From: Scottsdale Arizona
If you had changed it, I would have been concerned that the replacement wasn’t the correct length.
Thread Starter
Intermediate
Joined: Apr 2014
Posts: 49
Likes: 1
Years ago I bought a Comp cams H-roller 242/248. This is just when the first mush metal cores were being sold and they didn't have a warning about fuel pump rod type. So I was driving down the freeway and my motor started sputtering. So anyway I installed a new ac-delco pump and it did the same thing. I was dumbfounded!
It turned out that the POS Comp cams mechanical fuel pump lobe went flat and was barely moving the pump rod. I had to replace the cam and from that day on I have only bought billet steel cams and I use the Polymer fuel pump rods from Speedway motors.
I did consider just installing an electric pump instead of changing the cam, but I figured with my big springs the other lobes might go also.
It turned out that the POS Comp cams mechanical fuel pump lobe went flat and was barely moving the pump rod. I had to replace the cam and from that day on I have only bought billet steel cams and I use the Polymer fuel pump rods from Speedway motors.
I did consider just installing an electric pump instead of changing the cam, but I figured with my big springs the other lobes might go also.
Thread Starter
Intermediate
Joined: Apr 2014
Posts: 49
Likes: 1
so you just pull it forward toward the opening? it's tight down there, you can't really see what you're doing.
Dr. Detroit
Joined: Mar 2012
Posts: 10,097
Likes: 4,027
From: New Braunfels Texas
Please check the short length of hose from the sender to the steel fuel line. I had issues with my 66' and went around the world with it and it was a $1 hose deteriorated inside and closing off flow.....
Use Parker 3/8" Fuel Rated hose for piece of mind.
Something quick and easy to check.
The sock is also suspect sometimes.......I can see mine on my 72' from the top with a pen-light.......you may be able to too.
Jebby
Use Parker 3/8" Fuel Rated hose for piece of mind.
Something quick and easy to check.
The sock is also suspect sometimes.......I can see mine on my 72' from the top with a pen-light.......you may be able to too.
Jebby
Thread Starter
Intermediate
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well I replaced the push rod and installed a much better filter and that seemed to do the trick. For now anyway. Thanks everyone for the great advice. I wasnt a C3 mechanic when I started this project but I learn something new every day
Race Director
Joined: Jul 2004
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From: Scottsdale Arizona
