Guys im back again with a head scratcher. so my 65 pontiac bonneville with 4brl and Carter AFB carb is disturbing my peace and summer time cruising tranquility. it started by dying everytime i stopped. i got the carb back (i had removed it and delivered to shop). i put the carb back on and it still does the same thing: runs great when chokes on, but as soon as she’s warmed up, she’ll die. start-die, start-die. if you keep foot on gas, it runs and sounds great. i can sometimes cajole her into staying running for a minute or so while i look for leaks but thats it. What ive done: found and fixed leaks around carb base. looked for vacuum leaks in hoses, replaced dash-pot, reset timing to correct setting, attempted to raise idle. The raising idle one is the hardest. its DOESNT SEEM TO MATTER how much i loosen or tighten the idle screw, it doesn’t really affect the idle same with the rich/lean screws. I’ve been told Carter AFB idles are tricky, but man… Do you think it could be vacuum advance? I had some say check the “dwell”, and i will, but ive had other people say thats not it. it seems like a key clue that the idle screw doesn’t work to raise or lower idle, and its just been rebuilt. i was told that it was a clue that when i drive, it will die when i stop in drive AND in neutral. Also, idle doesn’t drop when i press brake, i was told if it did, that was a clue.
Is the choke fully open when it’s warmed up? Do you know anyone that knows carbs? I think a good hand could solve this quickly if they could get their hands on the car. I’m guessing some kind of linkage snafu. With some mis-adjustment thrown in on the side.
Questions. Is the business end of the base idle speed screw touching anything? If it is, the thing it’s attached to may be slipping on the throttle shaft.
Stallng when you step on the gas (Chevy experience) could be from a missing choke stove pipe or hose. You’re supposed to get some hot air all the time. The butterfly in the air cleaner intake snorkel should be closed on startup. It stays closed for only about 45 seconds; then the warm air closes or opens the plastic valve on the air cleaner housing causing the butterfly to open then you get the somewhat cooler air.
Stalling on stops could be related to no base idle. The screw might be too short from “unauthorized repair.” Then there may be frayed wiring in the distributor. Vacuum advance frays the wires by moving the breaker plate back and forth. I’ve only seen that on electronic ignition on Fords about 1985.
Also:Get a HOLLEY.
Yes, fully opened. carb masters are hard to find these days!
This site might help or at least give you some areas to check
I’d follow the troubleshooting checklist from that web site. Looks very thorough.
this one may apply:
Q: Why does my Carter AFB only idle with the choke closed?
A: This usually means the idle circuit is plugged or restricted. Cleaning the idle passages and jets should restore proper fuel flow.
also this:
2. Idle Mixture Screw Response
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Turn each idle screw in and out while running
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Engine changes = circuit working
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No change = plugged idle passage OR vacuum leak
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Hopefully, George will log in with some advice. IIRC, he has a lot of experience with carburetors.
Please, you beat me to it! I have a Holly on my old boat (with a Ford 351W) and it’s pretty trouble free. Also Edelbrock, I think they are based on Holly design.
No Holley for me, I had a Carter on my Plymouth, no problem.
Back to the OP. As pleasedodge van asked, is the idle set screw moving the throttle opening (butterfly)? Is the screw making contact? Do you have a vacuum gauge? Try to get a reading when the car is running. Pictures of the linkage would help.
If it were me, and I have the budget, would switch to throttle body fuel injection. If you want to stay with a carburetor, rather than rebuilding it again, buy a new Edelbrock carb which is a descendent of the Carter.
Have you joined a car club? You can ask there for who they use to rebuild their carbs. There are also shops you can ship it to. Any restoration shops near you? They might do it, or recommend somebody.
Another possibility: worn throttle plate shafts, no simple rebuild can fix that.
Vacuum leaks at intake gaskets, brake booster, PCV system if equipped, or to internal vacuum operated accessories like A/C system or power door locks are all possibilities.
I find the Carter carbs to be far more trouble-free than Holleys.
There’s a book on Amazon on rebuilding and modifying Carter and Edelbrock carbs if you’re so inclined.
1st of all, carburetors (carbs) are my Kryptonite, I can fight through them most of the time, but I lose some battles 1st… lol
Give me a transmission of that era to rebuild over a carb almost any day of the week (once on the work bench)…
Sounds like you sent the carb out for a rebuild because of the issue you are having now even after the rebuild… I would give the shop you sent it to a call and ask for some advise/help… If it was a local shop, I’d just get the vehicle to them and ask them to diagnose and or repair it…
Did you replace your fuel filter???
Since it seems to run well with the choke on and stalls with it off, once the choke pulls off (warmed up/open), try giving the choke a little enrichment to see if it will idle then or does it still die out… If it picks up and keeps running, that sure sounds like it is possibly in the idle circuit or a lean condition somewhere…
Even though the shop just rebuilt it, it is quite easy for a tiny piece of dirt or old fuel tank scale to lodge itself in the idle circuit channels the moment you start the car…
I’d also check the base plate gasket and make sure it is the correct one and sealing properly…
Plug off every vacuum port on the carb to rule out an outer vacuum leak. If it idles good with everything capped off, start installing one vacuum line/run item at a time until you find the issue…
I’d hold off on turning the two idle mixture screws all the way in for now. Since the carb was just rebuilt, I’d rather not change their baseline adjustment until we know what we’re dealing with. If you do test them, turn them gently and one at a time and pay attention to whether the engine reacts at all. If there is little or no change, that would make me suspicious that fuel isn’t making it through the idle circuit…
And if you have a vacuum gauge, this would be a good time to hook it up… The vacuum reading and how the needle behaves could tell us a lot about what’s going on…
My money is still on an idle circuit/lean condition or a vacuum leak somewhere. The fact that it runs great when you keep your foot on the gas tells me the engine itself is probably pretty happy once you get it off the idle circuit…
Good luck…
Just my experience. Whatever year it was, maybe 78, my mom had a couple yesr old Plymouth that was stalling in the morning after about five miles. I went through the carb twice with a kit and still stalled. My genius brother in law took a look and removed a coin like item on the manifold that operated as a heat riser for the choke. Worked fine after that. Sometimes we just need to expand our focus a little but for sure check the choke and mixture screws. They liked to lean that vintage out so much they would hardly run without advancing the idle.
I had a car that wouldn’t idle. Turned out my intake manifold gaskets were not sealing well. I had replaced intake 2-3 yrs prior and seems it was installer issue. I stored car in unheated space over winter and it didn’t like sitting. I agree, check engine vacuum.
The 1965 version of the AFB carburetor on Pontiac does not have a conventional base ideal speed screw. Instead, it has, on the carb base, between the idle mixture screws, a large screw that serves as an idle air bypass. This is the screw that controls the idle speed when the choke is open. The “fast idle” screw rides on the cam that is connected to the choke. The correct adjustment of that screw is 1800 RPM on the second highest step of the fast idle cam, after the idle air bypass has been adjusted to 550 RPM in drive. The 1800 RPM is to be set with the transmission in park or neutral. Check your timing and dwell before messing with the carb. Dwell should be 30 degrees with the vacuum hose disconnected and plugged.
thanks for your input. screw doesn’t do anything. no stall when hitting gas. screw looks very stock, and no reason to think its not. vacuum advance WAS broken, i figured that out. but because i have manifold vacuum, i dont believe that matters. however, i did order a new distributor yesterday. i dont believe thats the issue though.
This is the best advice ive gotten so far. so:
I did call the carb shop and they will take it back, but im going to try and figure it out first for my own learning.
i replaced the fuel filter about a year ago.
when you say “give the choke a little enrichment” do you mean just closing the choke a little bit to engage it?
Base plate gasket is on my list, i just got a new gasket. the kit only came with 1/4 inch riser, which is odd. so i used my old paper gasket, which isn’t ideal, so im going to do that.
honestly i can’t tell if riching and leaning it hels, because its extremely difficult to tell when its dying oiver and over, and when your foots on the pedal to keep it going, its hard to tell., which is the same reason its hard to use my vacuum gauge. i know the rich/lean at least works a little, or did, is because when i was able to use the vacuum gauge before this happened, the vacuum Would go up and down.
ill try again to find a vacuum leak next time im out there. it could be small enuff that starter fluid isn’t doing much. I did find a few leaks and fixed them though.
thank you!
thats a good idea. thanks.
i wasn’t aware i could visibly watch something move when i turned the screw, so ill try that. i do have a vacuum gauge, but what reading would i be looking for? ill try and get some pics.