Removing Fuel Pump on GTX

[Jc cooper]

I did not enter the discussion a while back about the fuel pump rebuild, but several things to think about. I disagree with then and now on the spring. Their spring choice is too soft. It works, but Carter designed the original to operate with the check valve springs and designed for the carburetors in use.

Yes the pump is a constant volume pump, but there is a velocity element to the stroke provided by the spring and that does effect the volume of fuel delivered especially at higher rpms. The pump arm pulls the diaphragm up primes the chamber with fuel, BUT the now compressed spring delivers the fuel through the check valves to the carburetor. Just like valve springs and cam design matter based on engine performance so does the fuel pump spring. At higher rpm the softer spring will not deliver the same volume and you also wind up closer to vapor lock on a hot engine when pump pressure is much lower.

There is information in the service manuals

Pumps are not hard to rebuild and it is Not easy to damage the diaphragm as stated, but there is a procedure for doing it. Also, I do not use the brake rivets as check valve. The umbrella seals had vapor escape holes drilled in them on certain pumps.

If you have an original Carter pump you can recover the spring and use it. I have extensively documented the cast part numbers, volumes, spring dimensions etc... for the various mopar original pumps. I really wish the current Carter would provide rebuild kits for the 8 screw pumps build to orig spec. But they don't and won't. I asked.

Then and now kits are good and do work, but they are not the same as originals.

Don't believe me. The 6903 and 4862 are the exact same body components with one exception. The spring rate. They have different volume rate. Not just pressure. There is a hell of a lot more technical stuff that went into the design to control spring harmonics and check valve flutter, etc.. Even the plates below and above the rubber diagram are sized and shaped by design of carter. They had a patent on it back in the day. I am sure the Chinese ignore all that and cut corners when making the current crop of pumps, but it mattered.

Can a proper carter pump allow fuel to bleed down or in other words, flow back pass the pump after setting for a few days! Also car has 3/8” fuel lines on both sides of the pump! FYI , what’s the cost of your replacement pumps! Thanks, JC

 

[Jc cooper]

Sorry 67 440 b-body

 

[Dragon Slayer]

It normally evaporates out the carb vents. Check valves are not perfect and with anti-percolator bleeds they can let gas evaporate after enough time sitting. Especially today's fuels. I am not a dealer, I do have hemi pumps I have restored.

 

[Jc cooper]

Ok thanks

 

[1969VAGTX]

Let me know when you get it off. Can get it taken care of and have pumps that are built already also.

Thanks. I have your contact info in my phone. Will follow up with you once I finally get around to removing the pump.

 

[Kern Dog]

I’ve never took the time to grease the rod

Let me know when you get it off.

 

[Nevada dan]

It usually gets off faster
LoL

 

[khryslerkid]

This is what Mike from Then and Now found in my M6903 Carter pump. You can see the oblong holes from the improper way the factory installed it. The spring was too heavy also.

Mechanical Fuel Pump 101

 

[Dragon Slayer]

You can't know if it is too heavy if it wasn't removed from the diaphragm and measured. You have to cut the assembly pull rod to remove spring. I measure the compressed height, then remove spring and measure spring length, spring rate. This allows you to know the preload. I have found original pumps to be consistent with spring rate, color coded springs, and compressed assembly length. Mostly 4024, a few 4862 and 6903. Hemi and 4862 used a brown spring at about 35lbf/in. The 6903 was blue 21 lbf/in. Then and Now was a 25lbf/in spring but was 1/4" shorter spring, so it has less preload.