Carter AFB Hesitation
 

Finally have my '64 on the road-photos to follow. The car has a 300 hp motor with a Carter AFB. When starting out, there is a hesitation that I don't know how to adjust out. The accelerator pump jets do squirt gas. Once it stumbles past the hesitation there are no issues. Any help is always appreciated.

Just guessing here, but there's usually an idle circuit, then a transition slot or circuit, then the main jets. As the throttle is opened, the transition slot comes into play.

I had this exact problem with a Rochester 2GV. The transition circuit was gummed up. A quick cleanout of that fixed the problem. I removed the carb to fix it, but you could take a shot by spraying some carb cleaner in the slot if you can reach it from outside the carb.

Does the accelerator pump discharge fuel from the squirter immediately? I went through this recently with the twin AFBs on my 66 Hemi Satellite. There’s a lot more things going on with an AFB accelerator pump and the idle passages than a person might suspect. My rebuild kit had 2 delay springs in them for the pump instead of a delay spring and the weaker pump return spring. That can really mess one up. And then there is a check valve below the squirter and one in the accelerator feed jet at the base of the pump well. If either of those don’t seal tight it will weaken the pump shot. And then the pump height is fairly critical as is the float height in the bowl. And then the idle and bleed passages in the primary Venturi boosters tend to get narrowed from dried fuel crud and have to be cleaned out. For the record, I never did get my hesitation completely eliminated although I did improve it considerably. The correct springs in the accelerator pump were part of it and then I installed larger bore accelerator pump shooters which further helped.

I found that carb cleaner spray will not remove those dried fuel deposits they need to be mechanically cleaned - micro drill bits and pin gages. The Carter Carburetors model data on low speed jet size, economizer passage size, Venturi part numbers, etc is very hard to find anymore. I don’t know if someone like Tbarb or another forum member would have access to the old Carter data. Your best bet may be to send it out for restoration to someone who will ultrasonically clean it or chemically clean it and go through it thoroughly.

Good luck.

A lot of motorcycle dealers have ultrasonic cleaners for carburetors. You might want to give that a try.

Provided this is not an ignition issue--

A part-throttle stumble on an AFB is caused by two things:

1) You have a aftermarket elastomeric accelerator pump, like the ones Daytona Parts sells. Get the correct, original-style leather pump with the garter spring which is still sold by many parts houses including Rock Auto.
2) You have an inferior check valve in the accelerator pump well, that does not have a properly calibrated spring or any spring at all (like the ones Daytona Parts sells). There is a gentleman on eBay who sells a correct check valve that works: https://www.ebay.com/itm/17151190739...oAAOSwpOxinTf8

Mikes Carburetors sells good rebuild kits with leather accelerator pumps. They also have replacement check valves. Just watch out for the wrong pump return spring. They also have a lot of how-to rebuild tips and problem solving tips on their website.

:iagree:
Mike's has good quality parts. My problem ended up being jet and metering rod sizes. It was way too rich.

Timing will cause a bog also, but describe your 'starting off'. Are you stabbing the throttle from an idle or does it happen no matter what rpm you are at when cruising?

Some good posts. I like Duck's suggestion of cleaning out the transition circuit. What you are experiencing is what a lot of people who run Weber IDA carbs experience, especially those that are set up for street use. In the case of the Webers, one needs to drill a third transition hole to eliminate the stumble. People play around with jetting, air correctors, and e-Tubes, but it is the transition circuit where the problem begins and ends.

Moreover, it might be the easiest thing to look at, first, and attempt to correct before moving to other areas if that doesn't solve the problem.

I can't remember what I forgot, but cannot forget what I don't remember. :toetap:
There are 3 holes in the accelerator pump lever. The rod can be moved to the hole closest to the pump shaft for a slower shot and the hole farthest from the shaft for a long shot of fuel. Generally on a new AFB they come with the rod in the center hole. Also, if the S clip on the pump lever is in backwards, it will bind and push the pump shaft around and loose the seal on the leather piston.
Is the AFB new or one you have ran before? Have you looked here? https://www.edelbrock.com/edelbrock-...esource-center
Looking at the 64 AFB 3721SB, I have on the shelf, it only has one hole in the lever. You can disregard this if you have an original AFB except for the S clip.
Ron

Thank you all for your quick replies. Duck-I did check out Mike's Carburetor because I didn't know about the transition circuit. Will be following that up likely this weekend. Dansyellow, I will check out the rebuild kit from Mike's. I have a Daytona kit in there now.

Actually Ron it’s the other way on the pump adjustment but I turn these things around in my brain all the time. The closest hole to the shaft provides a longer pump shot and stronger squirt of fuel, but of shorter duration. The outer hole provides a shorter pump stroke of weaker flow but of greater duration. The middle hole is where the pump is normally specified to be set. Changing to another hole should be followed with resetting the pump height by bending the rod link. On my Hemi, I set one of my carbs on the inside hole and with a .033” squirter virtually eliminated hesitation - but in reality it’s sort of a way of masking over some other issue. But if it works short term to get rid of the hesitation then there’s no reason not to do it. Even though it shortens the duration of the AP shot by the time it starts to run out, the transition and power circuit may have already kicked in enough to make up for it.

I second that timing, fuel bowl float level, clogged idle/ transition circuit, lean primary power jetting/ rod combo are other possibilities.

And yes, the “S” clip should look like an S when viewing the carb from the front and not as a backward S.

Just a follow up. Thank you all for your input. I did a conglomeration of all of your suggestions. I bought a Mike's carburetor kit and the cleaning brushes. Went nuts with all of the nooks and crannies. Had to get is adjusted and the automatic choke needs more adjustment. The car has a 300 HP set up but the cam is a bit hotter. I checked the timing and it was at 8 degrees as recommended with the vacuum advance disconnected and plugged. Set it at 10 degrees and it is running well. Thanks again everyone. Now I have an oil leak to chase down but this is for another day. .

What VAC can is on it?

my original crapped out and I don;t recall on the VAC can.