VCCA Home Forums TECHNICAL - 1945 AND EARLIER 1929-1932 Carburetor Accelerator Pump - 31

Rebuilt my carb (1931 updraft) using kit from Filling Station. Replaced the accelerator pump leather, but fuel is leaking out the top of the pump when I press it. Must have installed the leather incorrectly. I can not find a good picture of how this leather is supposed to be installed. Can someone provide a description of this? Thanks!
Joel Roper
Plano, Texas

Hi Joel --

The accelerator pump seal is a leather cup expanded by a small coil spring. The cup is attached to the pump piston with a screw and the lip of the seal should face downwards with the small expanstion spring inside. When inserting the piston into the bore of the pump, one must be sure that the lip of the seal is not folded back or damaged or it will leak. To do that, you first need to lubricate the bore lightly with some oil and do the same to the leather cup. Then, compress the cup to the same diameter as the piston using VERY thin (.005" or less) either plastic sheet or shim stock. Slide the piston with plastic/shim into the bore and gently remove the plastic sheet or shim stock. It should then work fine.

While you have the piston out, check that the bore of the pump cylinder wasn't damaged or burred and be sure that you didn't damage the leather seal the first time you assembled it.

Hope that helps. Good luck with it, and welcome to Chevy Chatter II! If you want to get tons more technical advice and enjoy a club of fellow Chevy enthusiasts, join the VCCA. You're welome here!

All the Best, Chip

Also, make sure that you installed a new rubber boot on top of the accelerator pump cylinder. The rubber boot seals off the top of the accelerator pump cylinder.

When installing the acclerator pump plunger and leather into the accelerator pump cylinder, I always use a Carter pump loading cylinder, that way the accelerator pump leather is installed correctly every time.

It is necessary to clamp the upper portion of the leather between the plunger body and screw. The spring holds the leather against the bore. I have found the leather installed incorrectly on many occasions. Also found most pump cylinders have a rough inside surface that is sure to leak. You may be able to smooth it enough with a brake hone.

Thanks, Chip. I will try that this afternoon. I had used plastic sheet to compress the leather the first time, but it was more than .005" thick and would not fit all the way in.
Joel

Are the Carter pump loading cylinders readily available? I saw it in the instruction sheet but not in the catalog.
I'll have to get a new boot since I didn't get one the first time (meant to put it in my shopping cart and then forgot).
Joel

I think the hone I have might be small enough, so I will try that as well.
Joel

One other thing, the only jet I could not remove from the carb was the accelerator pump jet. Most of the jets were difficult to break loose, even with penetrating oils, but this one would not budge. I did not see it listed in the catalog, so I made sure not to destroy it trying to remove it. If this were clogged, would it cause the pump to leak?
I just checked, and there is no gas coming out of the jet when I press the pump (obviously should have done this test before assembling everything). Would this be because the leather is not sealing, or would the leather not be sealing because the jet is clogged?

The accelerator pump jet has a itzy bitzy hole (0.021" dia.). If it is plugged then the pump will not squirt gas into the carburetor throat. Removal of the pump jet can be difficult without the correct tools and knowledge. I don't know of a way to clear it without removal and taking it apart.

If installing a carburetor kit (actually only a few gaskets, plunger leather and a nearly worthless new needle and seat) does not solve your problem, it is best to send to a qualified rebuilder. There are two that haunt this site regularly. Either of them will do a first class rebuild.

Some of the carburetor kits on the market today for your carburetor are just about worthless, other than the accelerator pump leather. And, the accelerator pump boot should came as part of the repair kit. However, from what I understand the boot has to be purchased separately. Also, Chipper is correct, the needle and seat supplied in these kits are pretty much worthless as well and I won't use them.

On the Carter pump cylinder loader, they are not available. You would have to find a used one or purchase a Carter tool kit that contains the loading cylinder at a swap meet.....and those tool kits, when found, are usually very expensive.

To properly rebuild your carburetor you have to remove all of the parts from the carb. body, including the venturi, choke cone, standpipe, pump jet, low speed idle tube, and etc. Without removing all of the parts from the carburetor you are pretty much wasting your time on a "rebuild". And, with your pump jet orifice being plugged and not working correctly, that is probably the cause of your fuel coming out of the top of the accelerator pump when the pump is activated.