318 stalling from idle

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aValiant318

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Good evening all. I have a 64 Valiant with a "70s 318 bored. 030 over, 273 heads" that I just bought. I put the engine specs in quotes because I haven't confirmed anything yet. My current pressing issue is that once the motor is warmed up, she likes to die from idle if you only give it a bit of throttle, but she's okay if you step on it. This weekend I plan to do a quick tune on the carburetor to get it to a baseline, but I was wondering if anyone had any thoughts or experience with what I'm experiencing that could offer some wisdom. I haven't gotten into the fueling yet, although the fuel filter itself is very clean. My very limited and inexperienced initial thoughts are either the carburetor or the timing is off. Thanks in advance everyone!!
 
remytherat said:
What carb? Sounds like a lean accordi
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remytherat said:
What carb? Sounds like a lean off idle stumble
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Supposedly it's a rebuilt Rochester Quadrajet. I just bought the car yesterday, and with life and kids haven't had a chance to research part numbers and all that jazz. I was planning on doing a quick tune up on the carb tomorrow afternoon to see if that smoothed things out before I start diving deeper. I did buy the car knowing it had an exhaust leak, so there could be vacuum issues I guess. Other than the stumble on light throttle issue, the car seems happy.
 
Move the throttle lever by hand slowly while looking down the carb (engine off) . Does fuel squirt as soon as you start moving the throttle? If not that may be your issue . The accelerator pump needs to be adjusted .
 
Photo of the carb setup would help immensely
 
Count the turns on the 2 idle circuit screws when turning them down to bottom.

Then take the idle circuit screws all the way out, spray carb cleaner in the 2 holes. then blow them out with compressed air after a few applications.

Polish up the needle ends of the screws with Scotchbrite pads and carb cleaner, wipe clean and reinstall to original setting depths.

Now you can fine tune them in one at a time. Screw them in until the engine starts to shudder, then back them out one full turn to give it the fuel it needs when idling.

Will help transition from idle to opening the butterflies after cleaning those ports and screws.

Good Luck

2 bbl BBD mopar stock 318 carb.


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So I was told it had a Rochester 4 bbl, but upon actual inspection, it's a Carter AFB. It does squirt fuel when the throttle moves and the cars off, so I can at least rule out the accelerator pump.

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Does the accelerator pump have a good strong shot? And does it begin as soon as the throttle moves?
 
remytherat said:
Does the accelerator pump have a good strong shot? And does it begin as soon as the throttle moves?
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1967 383 AFB had a special leather accelerator pump smaller diameter than like a 1406 Edelbrock I am used to working with, with the rubber Seal.

Leather seal could be getting dried out. Took a lot of hunting to find one of those but found one for the one I cleaned and rebuilt.


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My guess is that the transfer slots are too far closed;
One way to tell, is if the mixture screws are open significantly more that 2.5 turns. If so;
Increase the idle rpm, then retard the timing, little by little, until it goes away. then close the mixture screws down to about 2.5 turns and repeat.
Other possibilities are;
that the fuel bowl is not properly ventilated, or
that the WET fuel level is low, or
that the fuel is stale. The fuel should be clear as water.
 
It looks like your vacuum advance is not hooked up correctly. It requires ported vacuum usually from the front of the carb where you have attached the choke pull-off. That diaphragm requires full time vacuum. With vacuum hoses improperly connected, re-check your timing, maybe 6-8* advanced. Advance and choke diaphragms are crossed. No spring belongs on the choke linkage.
 
Thank you everyone for all the advice so far! This is my first carb car, and since I obviously bought it used (I wish I'd bought it new, I'm sure it was cheaper in 1964), I have no idea what's been done to the motor, and more importantly, what's been done incorrectly. I really appreciate everyone weighing in with their thoughts, and I'll be sure to update the thread as I check things off the list. Merry Christmas to everyone!
 
Murray said:
It looks like your vacuum advance is not hooked up correctly. It requires ported vacuum usually from the front of the carb where you have attached the choke pull-off. That diaphragm requires full time vacuum. With vacuum hoses improperly connected, re-check your timing, maybe 6-8* advanced. Advance and choke diaphragms are crossed. No spring belongs on the choke linkage.
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Good eye! At least someone is actually looking instead of shooting from the hip. That's the first thing I would do. Swap the vacuum hoses from the distributor and the diaphragm. I would also reset the timing as well, because you will no longer have manifold vacuum on the distributor vacuum advance.
 
That carb may not be for a 318. Certainly not original for a 1970 318. Carter made 505 variants of the AFB, each one essentially custom 'tuned' for the engine it went on.
It is probably a Mopar carb because it has the 3 step metering rods [ raised covers on the met rod pistons ].
Loosen [ not remove ] those covers & swivel to one side; make sure the piston moves up &down freely [ there should be a spring under the piston ].

A 4 digit carb # should be stamped on one of the carb's mounting feet, starting with a 3 or 4. What is it?
 
Here's the number from the carb. Again, I know next to nothing about this setup, so I'm flying blind here, even if I wasn't a carb beginner.

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Originally off a 1967 273 man trans. Original jetting: 0.089" pri jet, 0.074"; sec jet.
#403 rods, 069/058/065. I am not sure if the power step is 0.065, or a misprint in my catalog. Very strange for the power step to be larger than the middle step.
This carb should work ok with some tuning.
 
The manifold vacuum advance is consistent with AJ’s theory about the T slot exposure. Float level is also worth looking into
 
All of you are simultaneously showing me just how little I currently know about carburetors, and providing me with a wealth of great information. A lot of this is out of my depth at the moment, but I'm looking forward to learning all of this stuff. If a simple tune up (one of the few things I DO know how to do with a carb) doesn't solve my issue, I've got a bunch of different threads to pull on. And even if that is the easy fix, you guys have given me a ton of information to research, learn about and become proficient in. Again, thank you all!
 
Intake manifold has no provision for heated choke. Manual choke cable incorrectly installed. Replacing the carb for one with an electric choke might be wise.
 
I did a tune up of the idle circuit, and that seems to have resolved my issue, at least for now. Time to dig into all of the other things you all have suggested or noticed are wrong. Part of the fun of buying this car is I have no idea what the previous owner did, and whether he did it correctly. Time to play detective! Thanks again everyone for helping me out.
 
That is indeed a 1967 AFB 273 carb for a manual transmission without CAP. I have 4 of them. The original rods should be Carter #16-403 which are 3 step rods .069 x .065 x .058 diameters, definitely a misprint. They are a very good carb, but the choke pull off should be removed and saved in a baggie with the attaching screws since there is no linkage to the choke shaft. Or leave it and use a cap to block off where the distributor vacuum canister was on the carb. Next connect the vacuum canister on the distributor where the choke pull off hose was on the carb. Check and reset timing to at least 10 degrees before TDC. Do yourself a favor and get a 340 accelerator bracket, Mancini Racing - Throttle Cable Bracket . I always run a choke, but not sure how with that intake manifold.
 
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