Developed a leak at the lower gasket on the pump. I took it apart to clean out the old gas. Its been sitting 1 year with only about 1 hour of use on the pump. When I removed the lower portion I found a black square hard sponge. Ive never seen this. Could this have caused a problem with the check valve, which caused the leak? HELP

i actually think the "sponge" is some sort of noise suppression. i've taken them out and now i hear the pump thumpin. leak is probably uneven mating surfaces. anymore i run all the mating surfaces over some wet or dry emory paper to get hem flat. i've had good success doing that and have picked up 1/2lb pressure doing it.

It is a pulse damper to assist the air dome diaphragm from collapsing too much on the pressure stroke. Not all pumps have it. When you say leak, what type of leak? Internal into the isolated chamber or external to the pump.

Gas was actually coming out of the lower gasket. I thought the check valve was clogged. Took it apart and it all gaskets looking good.

Any screws loose when disassembling? The bottom surface looks good other then the center bridge. The pocket with rubber should have been dry. What does the top and bottom surface of the middle body and top look like?

All surfaces look good. Should that middle area be machined? It looks as cast. I think gas spilled into that chamber when it was disassembled.

i think if you run the mating surfaces over some emory paper on a flat hard surface you'll notice that the surfaces aren't always true. they are "as cast" surfaces; don't trust them to be flat.

As stated it needs to be flat. If a high spot the middle section won't be a flush seal it would pivot slightly on the high spot. That might be your issue. You do need to check carefully for cracks at the fitting bosses. Over tightening the pipe thread fitting can crack the aluminum casting.

another thought; the "bowl" is on the suction side of the pump. the chamber with the black sponge should always be dry and the chamber under the two valves is wet but not under pressure. the middle valve section of the pump above the bowl is pressured. i wonder if your "leak" is coming from the pressure side and not the suction side? i would carefully examine this area. after all any fuel leaks there will pond around the bowl.

I was going to post this same question about the sponge.
Since not all pumps have it, is there a downside or advantage to leaving it out?

The flat smile shaped airdome diaphragm service a few purposes beside isolating the suction and pressure side of the pump. It is meant to give into the dry chamber when the plunger comes down generating the pressure stroke. This flexing reduces the max pressure at the beginning of the stroke, and toward the end of the stroke as pressure is reaching it's lowest point returns to it's original position which smooths out the pressure pulse and extends the movement of fuel out. A trick to raise pressure on a pump with low output pressure would be to double up that diaphragm. Or reduce it's inward flex with the hard sponge.

all carter 3 valve pumps i've messed with have the sponge. i take my pumps apart and re-work them and don't put the sponge back in with no adverse effects. i say keep it if you want, remove it if you don't; hasn't made any issues one way or the other for me.

Thanks guys! Im going to wet sand it flat and see how it works.

If you are dealing with original fp from the 60s and early 70s you won't see that foam. Later version and the 6903/4862 you will, but not always.

factory 2 valve pumps don't have the chamber so a sponge couldn't be installed.

Of course. I am talking about rebuild able pumps. 4024, the 2500 series, even very early 6903. Plus the marine pumps. I have disassembled and documented many of the Carter orig pumps. Cast number, part numbers, orientation, volume, spring pressures etc...

what are the spring pressures?

4024 orig hemi = Brown spring 35lbs/in 2.0625” L x .9375”OD; Compressed length = 1.625” = 15.3lbf preload

6903 = Blue spring 21lbs/in 2 9/32” L x 15/16”OD

4862 C9 = Brown spring 30lbs/in 2 1/32” L x 31/32”OD

Do you have this info for the 6270 small block pump?

Top: MO-3032 12 (Bulge and multi holes)
Middle: M80-730 R 8 C Round shaped cavity OD 3.5”, ID 2 9/16” Hole ring dia 3 1/16” 1/4" NPT
Bottom: M118-276 3 C R (Different Design no boss C R/90 Clocking/Course Thread) Modified opening
Lever: 177-381 Lever Spring Gray 1.55”L x .390” Dia
Diaphm: None 364 Stud 2.20” OL stud, 8 hole 3 5/8” OD, 2 3/16” Lower Disc, 2 3/16” Upper Disc, Steel Spring

This was a pump with no date code, but the later manufacture with bulge on Top that marine pumps would have a vent installed. The Bottom was modified outlet to accept larger fitting by previous owner.

I did not cut off rivet to release spring and measure it.

The other portion of the diaphragm that effects volume and pressure of the pump is those steel disc that sandwich the rubber diaphragm. They are actually different diameters on original pumps depending on the model. They also have stamped ridge that had a patent by orig carter. If you think of the captured volume of fuel in the pump outlet chamber under the diaphragm when pulled up fully the size of that washer determines how much outside area of the diaphragm can actually stretch, tapered volume and what is solid surface for the built up fuel pressure to resist the downward push of the spring.
I have post picture of chamber before, here they are again. Notice gear shaped hemi chamber which increases volume under diagram per stroke, which also would lower pressure required to stop stroke when carb needle closed. Hence the larger spring force to compensate. I also have seen orig hemi with extra washers under the stud to increase preload of that specific spring. Also notice the bottom of the hemi pump does not have to have inlet fuel flow through a casting to get to chamber. The inlet fitting opens directly into the inlet chamber.

The round chamber is the typical 6903/4862/6270 modern pump parts.

Dragon, What can you tell me about this pump?

more pics

Carter 3497 71-75 Freshwater 361/440 Marine and Industrial pump. Did you get that one off ebay? I was going to buy one to open it up, but they sold out. Take it apart and tell me the internal casting marks in the middle section and bottom. The Top has the hemi casting. That serial number after the 3497 is a much later 2000 date code serial data. Would be a good BB pump, and depending on the internal configuration and spring, may be Hemi type, or just a normal pump like the 6903. But considering marine use may very well have a higher volume per stroke.

has anyone had to grind on the pump casting or engine block, when changing to a carter pump from a crimped together factory low performance pump, to get the carter pump to fit flush with the mounting pad on the engine block ?
i picked up a chromed carter pump that looked almost new, cheap, at a swap meet one time. i went to install it on a mock up block, and couldn't get it to fit flush with the mounting pad. it appeared it could fit if either the pump ear or the block [or possibly both] were ground down a bit, but i didn't bother because i just bolted on a crimped style pump. no pump push rod was involved because this was a gutted block.

Not for the types shown they all fit fine. The race pump 6 value unit, and I guess some of these knock off types may be larger and require that. I have installed plenty on built motors no issue. These rebuildable types were standard on the early engines and hemi.

Coated all the surfaces with Dykem then sanded every surface flat. There were a few definite low spots. Haven't checked it yet.

dragon slayer - can you find out anything on this pump?
It's for a small block.

No I focused on the big block especially hemi type. Looks period original and the F3 date code would be Jun 63. The carter book has it for a Dodge Desoto and truck starting late 1957. Listed as a 5 to 7 psi pump. The mopar service manual have the carter pump number so you could look up for more specifics.