Carter AFB woes

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BCjohnny
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Re: Carter AFB woes

Post by BCjohnny »

And maybe add to the discussion .....

Are the engine mounts knackered, or metal on metal ? Causing running vibration to unsettle the needles and seats ?

Completely different set up but years ago the only way I could 'calm' the carb down on a particular application was to monkey about with the mounts

WAG but might be worth a look as everything else has pretty much been covered
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Re: Carter AFB woes

Post by mag2555 »

If the 1963 Pontiac 4 bbl 195 cid 4 cylinder ( 1/2 a 389 engine )which was a vibrating mess of a motor could run a AFB carb Then we can rule out vibration as the issue!
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BCjohnny
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Re: Carter AFB woes

Post by BCjohnny »

mag2555

I've spent enough time around throbbing 4 cyls ....... out of imbalance secondary rocking couple twice crankshaft speed ...... O rings & Thackery washers etc etc to understand the problems

Just because one application runs ok, half of a V8 in this instance, it doesn't necessarily mean they all will ....... hence the caveat 'WAG' in my post ......
Sterly
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Re: Carter AFB woes

Post by Sterly »

Thanks everyone for the comprehensive replies.

One thing that puzzles me is that many respondents are talking about checking the idle air bleeds whereas I thought that for the primary mains to be starting early then if the problem is in the air bleeds it would be the main air bleeds, not the idle. Am I correct or am I misunderstanding the way the system works?

Thanks again
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Re: Carter AFB woes

Post by rebelrouser »

best explanation I ever found. The AFB's used on factory cross rams I believe had three air bleeds.
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Ishiftem
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Re: Carter AFB woes

Post by Ishiftem »

The labeling in that photo is wrong. The little tube on top of the cluster is the primary main air bleed. The drilled hole on top of the cluster is the idle air bleed. The little brass pressed in to the side (not shown) is the secondary air bleed.
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Re: Carter AFB woes

Post by Geoff2 »

BC,
Thanks for the 'black line' tip.
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Re: Carter AFB woes

Post by Geoff2 »

Ishiftem is correct.
Another problem is that the diagram is from Edel & they use different terms than Carter did. Carter called the internal Idle channel restrictor the Economizer, because it controlled the volume of air + fuel delivered to the idle system, & a LOT of cruising [ economy ] is done on the idle cct.
The 2nd idle AB is called the Bypass air bleed in Carter lingo & is on the side of the booster [ not visible in the pic ].
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Re: Carter AFB woes

Post by rgalajda »

" Anyway it cleaned up well and with a carb rebuild kit ."

I have restored some of these old carter carbs ( not this particular model 3131s ).
It is hard to imagine that it cleaned up well. These 60 year old carbs always/usually need a complete media blasting to remove corrosion inside of them after a cleaning in the sonic cleaner and all passages checked to be open, including passages to and from the clusters. Including passages to the idle mixture screws.

Was the gas tank and fuel lines cleaned ?
To test the brass floats . Boil some water and turn off the element. Submerge the float for a couple seconds and watch for air bubbles. If no air bubbles appear , float should be good. If air bubbles appear , the float has a leak that will take on fuel. The air bubbles are easily visible.

Engine condition and ignition system to be in good order addressed first.
You have to get a good idle next.
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Re: Carter AFB woes

Post by golden_commando »

Some older Afbs use different floats than AVS/Edelbrock ones, also the cluster is lower on the carb too, how height are you setting the float? The main air bleed should be around .031in. If you change the needle and seat do know if they have the same size or bigger?
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Re: Carter AFB woes

Post by mag2555 »

This may help?
Here is 4 photos made out of one to give good detail.

Also note that if the carb has a hot idle air bypass on top the secondary’s, then that needs to be held closed when making idle settings.
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Sterly
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Re: Carter AFB woes

Post by Sterly »

Thanks for all the replies. Here’s a bit more info:

floats checked in warm water - both OK

not sure of inlet seat size (I can check) but they came in the rebuild kit. I’ve also tried running the old ones - problem still there

float level and drop checked multiple times

floats are parallel with sides and as far as I can tell move freely

main air bleeds cleaned and open, however what I think is the main bleed on each cluster that uses the long tube look partially occluded round about where the tube meets the body of the cluster (I think I got that description right!). I can still get wire through although you can feel a sort of ridge at that point. Because both primary clusters are the same in this respect I assumed that’s how they should be. Amazingly, the workshop manual actually details the sizes of the bleeds so I’ll try measuring them with some small drills.

There are gaskets under the clusters and I’ve paid close attention to fitment and I’m sure they’re right.

The gas tank was cleaned out and all fuel lines, filters and fuel pump were replaced.

Thanks for the excellent assistance
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Re: Carter AFB woes

Post by Geoff2 »

Keep us posted, thanks!
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Re: Carter AFB woes

Post by rgalajda »

"floats checked in warm water - both OK"

I hope you meant Boiling water
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Re: Carter AFB woes

Post by winr »

Do you have a vacuum gauge, if so.. hook it to manifold vacuum and watch what it reads when engine is running and also when engine starts to die

ALso, when engine is running, slowly close choke and see how it affects engine/idle
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