AFB Question

[Christopher R.]

Rebuilding my 9600 series Carter AFB carburetor. Winter project. Question concerns the accelerator pump. In putting the carb back together, I noticed that the accelerator pump cup seal does not make contact with the sides of the bore. It pretty well fills the bore. But it doesn't seal against the sides. That doesn't seem right to me. I forget how it was when I took it apart. The carb worked fine last Summer. No bog on acceleration or off idle. It's been dry since then. The carb has only a few thousand miles on it, but it is pretty old.

The leather seal is supple. The spring is in place underneath the spring. The assembly goes up and down nicely in the bore. My instinct tells me that this leather seal is supposed to seal against the sides of the bore, forcing gasoline down when depressed.

Is it possible that the leather will swell to seal off the bore when it sits in gasoline? Will the cup sides flare when the plunger is depressed?

(The rebuild kit I bought was for an older series AFB. Rebuild kits do contain new accelerator pump plungers. But the old ones are a different size than the new ones. (Bores are bigger on the new ones.))

[Roy B.]

Re: AFB Question

Yes the leather seal will swell , you could let it set in gas for a while then try it.

[Bruce Boatner]

Re: AFB Question

Chris,

I had the exact same question when rebuilding my AFB. Mine is from a 1964 327/300--not sure if it is a 9600 series or not. The old leather seal was pretty messed up so I could not use it as a guide. The leather and rubber seals on the new pump I installed did not make contact with the bore exactly as you desribed. My assumption was that after coming into contact with gas the leather would swell and provide a good seal. My car had a very bad hesitation problem from a dead start before I rebuilt the carb. The hesitation problem improved quite a bit after installing a new pump, but the car STILL hesitates (see thread below). The new pump I installed does seem to provide a pretty good pump shot, but only when I move the pump fast. If I move the pump slowly, I cannot tell if any gas is squirting out all.

Your post has me wondering if my hesitation problem is due to a "loose" pump, or if it is normal for the pump seals to appear loose when everything is dry. If you experience a hesitation problem after putting everything back together we know the pump is the problem.

[Christopher R.]

Re: AFB Question

I don't remember how the pump plunger fit when I took the carb apart. I do know that there was no off-idle hesitation on acceleration ("bog") when the carb was on the car. The work I'm doing on the carb has nothing to do with the accelerator pump. The exact same plunger is going back into the exact same carb body. I thought it odd that the plunger didn't seal the bore. Hope it does after I put it back together and it sits in gasoline.

I assume you've seen all the adjustments for the accelerator pump in the literature. As I understand it, they are:

1. height of the tip of the plunger from the top of the carb;
2. which 1 of the 3 holes in the lever; and,
3. bending the rod from the throttle.

From the posts below, I understand that you have eliminated other possible causes of your problem. So your problem seems to be carb related, most probably the accelerator pump.

Could be the adjustments outlined above.
Could be the plunger. You can buy new ones for ~$6. Email if you want a p/n. A new one should have come in the rebuild kit.
Could be the pump jet housing. Did you rebuild this carb? Maybe you screwed up the little gasket that goes underneath the housing? I believe there are a few versions, all of which are contained in rebuild kits. You should have some left over. Maybe you used the wrong one, and it's blocking a hole.

Again, I'm no carb expert, but I know that an accelerator pump circuit on any carb must immediately give the proper shot of gas when the throttle is depressed, or the car will bog. You state that you get gas when the thing is depressed quickly, but not slowly. Hmmm, that doesn't sound right. You've gotta get a measured shot of gas immediately when you hit the throttle.

[Mike Geary]

Re: AFB Question

Guys:

My rebuild guide states that before installing the accelerator pump, you should soak it in gas and once soft, you should "flare" out the bottom of the leather cup with an awl-like tool. That is, put a lip on it like the bottom of a bell.

Made all the difference on my AFB 3721.

Mike

[Clem Z.]

i do this but i use oil incase the carb sets

awhile before using and the gasoline soaked leather will just dry out

[Verne Frantz]

Re: AFB Question

Chris,

There are two types of leather skirt accelerator pumps being made. Most kits use one with a short skirt (fine on a trim young woman, but not for a good running AFB)
I use ones made by Walker Products, Los Angeles, CA, 323-232-3359. They have the correct longer skirt, which will seal better to the pump bore. I also soak mine in ATF for a day before installing them. I learned that trick from Bob Kunz (credit where credit is due)
Verne.

[Christopher R.]

Re: AFB Question

There's a marine version of this accelerator pump. Costs around $15. I believe that the difference is that the "skirt" is made out of neoprene.

[Bruce Boatner]

Re: AFB Question

Per my Carter Carburetor book I bought this weekend, the fit is supposed to be somewhat loose so that not as much gas is pumped when the throttle is LIGHTLY depressed. Theory is that vacuum will have enough time to catch up and engage the main circuit without wasting gas. By the way, be sure to put the s-link in the proper position on the pump rod and pump lever. Turns out that was what created my problem (see earlier post). Who woulda thunk it?