63 AFB Idle Problems

[Wayne P.]

Installed a restored AFB on the 63. Idled fine with only a minor idle screw adjustment. Fast forward 3 months to first road test(nice weather). Absolutely will not idle. I'm not very familiar with AFBs. Any ideas for correcting the problem?

[Duke W.]

Re: 63 AFB Idle Problems

Which engine?

What's the carb number?

Does it have the correct OE cam?

Does it have the correct "gasket/component stack" between carb and manifold (see AIM)?

What's the number stamped on the VAC?

Do you have a '63 shop manual?

Have you gone through the idle speed/mixture adjustment procedure?

Duke

[Timothy B.]

Re: 63 AFB Idle Problems

Wayne, If the car starts and fast idles OK then it could be the choke not opening. Try the simple things first. Has the car sat with the same gas for some time? Does it sound like it's flooding or just wants to stall when you let the car idle? Post as much info as you can, someone usually will give good direction.

[Wayne P.]

Re: 63 AFB Idle Problems

Please read it ran fine when first installed. After sitting for 3 months with no changes, it will not idle cold or hot.
It's a 340 hp with 70 LT1 cam. It has the vac advance that Duke recommends. I have the service manual. I followed the procedure listed. Shouldn't make a difference, but for full disclosure of info, the engine was rebuilt just before the initial install. It has about 100 miles on it before having the carb restored.

[Jack H.]

Re: 63 AFB Idle Problems

Have you pulled the air cleaner and visually inspected what's happening with your choke? If it's not moving freely and crisply into its cold engine firing position, then opening up in proper response to: (1) the vacuum operation of the carb's pull-off mechanism, and (2) the heat activated release of the divorced choke mechanism, you've got a good starting point for finding/fixing your problem(s)....

[James G.]

Re: 63 AFB Idle Problems

God forbid if the new corn fed gasoline created the problem ??

[Duke W.]

Re: 63 AFB Idle Problems

Still not much to go on here...

With a "B28" VAC, LT-1 cam and 10-14 degrees of initial timing the engine should idle acceptably at 900@12", and total idle timing should be in the range of 26-30 degrees. Initial setting on the idle mixture screws should be 1.5 turns out from the seat.

The choke mechanism should be checked (including the integrity of the heat tube in the exhaust manifold) as others have suggested and a thorough check for vacuum leaks should be conducted including the VAC.

A Mighty Vac, dial back timing light, and a propane source are what is needed to do these checks.

Evaporated gasoline can leave deposits, which can eventually foul the tiny air bleeds that are critical to proper carburetor operation, but it usually takes years for this to occur - not just one period of inactivity after a rebuild.

Duke

[Wayne P.]

Re: 63 AFB Idle Problems

Hated to, but pulled the new carb and disassembled. Didn't see a thing wrong with it, but now idles fine. Took it for a short ride. Next problem, now,as before restoration, power is weak and worse yet, is the surging at less than 2,000 rpm. I've had 340hp before and they did not run like this. While I had the carb apart, I checked jet and metering rods to be correct. Other ideas?

[Duke W.]

Re: 63 AFB Idle Problems

What pistons are installed?

What's the head gasket thickness?

Was the actual CR computed? What is it?

What work was done to the heads?

What is the complete spark advance map specification?

Has the engine been tested on a chassis dyno with a wide band O2 sensors? Results?

Duke

[Timothy B.]

Re: 63 AFB Idle Problems

Wayne,
Have you done any work on the distributor other then the vacuum advance, if it's a stock 63 distributor then a recurve may be in order. Total centrifugal is 24 and all in by 3000 RPM is good and 14 +- initial advance to yield 38 total timing. This will make the engine run better but I don't think it has anything to do with your surging.

I believe the stock jet for 3461S is .104" and 16-389 (.060/.069) metering rod so I don't think it's lean. Some time ago there was discussion about surging exactly like your experencing but I don't remember if that person ever solved his problem. Don't know how the engine could idle properly now if you did not change anything. Only thing I can think of is the bottom of the carburetor not flat from the heat/cool cycles over the years and repositioning the carburetor sealed vacuum leak.

If you hold the carburetor above your head and look into the bottom can you see light around the throttle blades with them closed? If you can, the blades are not sealing to the bore at idle and could be causing problems. (Don,t do this with gas in the carburetor!)

[Wayne P.]

Re: 63 AFB Idle Problems

Thanks for all the replys.

You can tell when it was restored the mating surfaces were squared. No modfications to the distributor except for the vac advance.

Duke, you ask a lot of hard questions.
It has factory pistons with fel-pro gaskets. I have no idea of the actual compression ratio and it has not been on a dyno. No work on the heads except a standard valve job.When originally put together, I remember the vac curve was pretty close to your recommendations. That was 4 month ago and I didn't write it down since I thouhgt it was good. I'll have to map it again.

[Duke W.]

Re: 63 AFB Idle Problems

I ask a lot of questions because without more information it's like throwing darts at a board blindfolded.

Duke

[John D.]

Re: 63 AFB Idle Problems

Don't discount the basics as discussed by others. You did see it was running fine at first. You could have some dirt or bad gas messing things up. Are you using any additives. Are you running 10% ethanol? You may be able to cheat a tad and put some good fuel injection cleaner such as STP in your gas. I had the same problem last Corvette Carlisle with my GMC. I mean the thing was idling and running perfect in spite of the 100 degree weather. All at once it took a crap and I do believe it was because of water in the gas or maybe dirt. The cleaner fixed it up in about 10 minutes. If you are running lead additives and have let the car sit 3 months that could be a problem also. John D

[Wayne P.]

Re: 63 AFB Idle Problems

It idled fine initially, but I never had a chance to drive it. It didn't have leaded gas. It didn't have any additives. No ethanol. Restorer has agree to take another look at it. I may send it back, but I would rather not ship it again.