Anybody messed with AFB's?

[DartGT66]

I've got a 625 AFB on my 318, otherwise it works very well, but the performance isn't as good as with the previous Dp Holley that didn't work otherwise. I think this is because the secondary air flaps opening too late. I think if they came in too early the car would bog, but it doesn't. It runs fine when the rpm is over 4000, but below that not too well; when I shift to higher gear the RPM drops down and the car slows down too. Have anyone experienced drilling the counterweights lighter to get the secondaries open sooner? How much did you drill and how did the car responce?

[toolman]

If it idles fine and takes off fine then I would try changing the jets first or the metering rods. Get the strip kit thru Summit or wherever and have at it. Be sure to write down what you started with and what you change to so you can go back if you have to. The secondaries are supposed to open by vacuum when needed, so it is automacally done for you. My 600cfm Elelbrock (same thing almost), worked good set up rich but it didn't like a rich accel pump shot. also make sure your fuel filter is changed often! The strip kit is about $38.

[DartGT66]

I have played a lot with vacuum secondary Holleys, and they have secondaries too that should open automatically. However, since they are universal carbs like the AFB, the secondaries open pretty late to avoid bogging. Getting the secondaries open sooner in a vacuum Holley ususally gives a dramatic increase in performance, and I think the situation would be the same with the Carter. Like I said, otherwise the carb works very well, there is no bogging what so ever, no hesitation, no flat spots. I think my problem has nothing to do with jets, springs or needles. Or do I just have to accept the fact that I have a ton less performance with the Carter than with a Holley?

[ehostler]

From your description, the primarys are not setup correctly for your engine. You need to tune the primary jetting and metering rods.

Ed

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'96 Dodge Ram 1500 SLT CC 360 4X4
'68 Charger 383-4

[DartGT66]

Like I said, other than lack of power, the carb works just fine. Do you think the carb is too lean or too rich? I still think the problem is secondary related, when I shift to higher gear at about 5000, the rpm drops to about 3000 and I almost feel the secondary air doors closing then after 4000 it runs fine again. I know the basics of tuning, and can't see how slighly off jetting would cause this situation. The carb is brand new and the jetting is out of the box. With the Holley the engine hesitated and bogged at normal traffic but at full throttle it run great through the whole rpm range. It was a mech secondary Holley replacement carb for a 327-402 chivy, so the tune was propably totally incorrect for the 318.

[moparking]

I have an A.F.B. on my 66 newport, and have had the opposite problem. I have a 2.76 gear,& a 4560# curb weight W/ a 383.It had a large weight and I still had to take out the secondary air valve and drill it out to add lead slugs, to get it to open more slowly. Unless carter has different air valves,you may indeed have to drill.The worst that can happen is that you will have to put some weight back in.

[hemi-1]

I don't claim to be a carb expert but I agree that the problem is the secondaries opening late. I just thought I'd tell you that the original AFB on my 59 Dodge (361) which probably is about a 400 cfm or so doesn't have any secondary air flaps, just the butterflies, which of course open manually!! One thing you can always try: take the air flaps out and see how bad it bogs. At least you could control the secondary openings with your throttle foot and maybe see if opening the secondaries sooner helps power below 4 grand.

[This message has been edited by hemi-1 (edited March 24, 2000).]

[toolman]

The strip kit offers a huge change in the size of metering rods and the spring kit adds even more possibilities. You probably won't even have to change the primary jets if it is already callibrated for power not economy from Carter. I changed mine in only one minute and you don't have to remove the carb from the motor. I would first try the .400 cruise step and mabe the yellow springs. Big differince on my car! and soooo easy to do! You could always drill later if you want to do some real work. I'm thinking it is lean on the cruise step (lower RPMs). How is the motor built? What cam, heads? I have been messing with my carb alot because I have had a backfiring problem and I think you might have been one of the guys that have helped me. Just want to say thanks. And now after seeing your info to pishta on the "advance springs", I'm thinking that might be another sollution for my idle problem. It wants to die under 900rpms but when I raise it to 1000 or so, it instantly revs to 2000. Untill I put in gear, then it drops to 1000 and slowly starts declining until it dies. Do I have to remove the dist. from the motor to check the springs?

[This message has been edited by toolman (edited March 26, 2000).]

[This message has been edited by toolman (edited March 26, 2000).]

[DartGT66]

The engine is a 318, 8.66:1 CR, ported 318 heads with stock size valves, MP 268/272 cam advanced 5 degrees, performer intake, 1 5/8" headers with 2 1/4" duals and of course the 625 AFB. I think I may try removing the counterweights and the airflaps for a try, and if I can get it pull through the rpm range in a promising way, I'll start drilling the counterweights. By the way, my original goal with the buildup was to get the same mileage as with the /6 while have 15 sec. performance. Haven't got any time slips yet, but the mileage is the same or even a little better. That's with pretty careful driving, but have to keep in mind that now the car runs better with a feather foot than with the /6 and a lead foot. The performance 'missing' when comparing the Holley and the AFB is so big, that it must be something alse than the jets. And Toolman, you have to take the distributor out to change the springs. Do you have a vacuum advance canister in use, and where is it connected to? That might also have something to do with your idle problem.