Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem
90% of 'Carburetor Problems' are 'Ignition Problems'
Kenth:
--- Quote from: Buick73 on January 10, 2026, 12:10:31 PM ---So, I understand that people are divided on rather the Pertronix is a 'good thing' or a 'bad thing'. But my original question was about the hesitation issue (please see original posts).
--- End quote ---
An engine must be in good mechanical condition (cylinder pressure) and have a well-functioning ignition system for the carburetor to do its job as intended.
A point breakerless ignition system where the ignition coil has too low an operating voltage will produce too weak a spark at the spark plugs and the engine will hesitate when the throttle is applied.
So, do you have good cylinder pressure and korrekt voltage to the ignition coil for the ignition system used?
Kenth:
--- Quote from: mcx on January 10, 2026, 05:13:26 PM ---…check the replaced air lid and verify it wasn’t replaced with the Buick 750cfm version, as those have the upper idle air bleeds in the air lid….the 800cfm version(7042240) do not have them in the air lid (unless custom modified)….Good luck.
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Only 1967 Buick Quadrajets has the upper idle air bleeds in the air lid.
Buick73:
--- Quote from: Kenth on January 13, 2026, 04:15:41 AM ---An engine must be in good mechanical condition (cylinder pressure) and have a well-functioning ignition system for the carburetor to do its job as intended.
A point breakerless ignition system where the ignition coil has too low an operating voltage will produce too weak a spark at the spark plugs and the engine will hesitate when the throttle is applied.
So, do you have good cylinder pressure and korrekt voltage to the ignition coil for the ignition system used?
--- End quote ---
Engine was completely rebuilt in 2018. 30-overbore (would have made 20, but pistons not available at that time). Stock cam. All cyllinders with about 180 psi. Coil voltage at 12V to distributor (no resistor).
Yesterday, I replaced all the ignition components- new 0.040-gap plugs (see picture of old ones), wires, distributor cap, rotor, & a new magnet wheel (one had fallen out).
While into the distributor, I noticed springs were worn/ stretched; weights were floating outward & not returning to fully retarded positions. I have a pack of various springs for it.
I put the stiffest ones in just to set initial timing (10 degrees BTDC). Then, I started experimenting with softer ones (mix & match). When I found the ones that I like for driving, I checked my results with timing light. I have 26 mechanical (so 36 total), all in at 3,000 RPM.
I also swapped out my vac advance (B9) for a B27 (5-7 inHg tip-in), 18 total. This is closer to the original spec sheet (please see attachment) than the recommended 'B1' (8-11 inHg tip-in), 16 total.
Carb rebalanced. I found best vacuum at 2 3/4 turns from seated. I returned both to 2 1/2 turns for best lean idle.
OVERALL RESULTS:
1. Part-throttle hill climbing has resolved. I can climb a hill easily without having to floor it.
2. Off-idle hesitation has improved, but is still there. Before, I was limited to about 25% throttle from a standstill. Now, I can push about 50%. Car accelerates smoothly & quickly 'gears-up'. I can feel mechanical coming in. Vacuum is probably contributing too after a few seconds as vacuum level rebounds with speed.
CURRENT QUESTIONS:
1. How do I improve the off-idle response? If I floor it from a standstill, car dogs forward for about 2-3 seconds, then winds up & starts moving (kind of like if I had just started with 50% throttle, except now I'm 2 to 3 seconds behind). Please see 'Results #2' above.
2. I've considered:
(a): Swapping more initial in exchange for limiting mechanical to maintain overall total.
(b): Installing softer distributor springs to bring advance in even quicker.
I currently don't have any knocking under any driving conditions, but I know I would have to be close with 36 total & another 18 vacuum. However, I never cruise at 3,000 RPM (that would be more than 90 mph for me). So, I would never see the technical 54 degrees.
Any other carburetor tuning I'm missing?
Thanks again.
Kenth:
To start with i would fix the mashed slot on air valve shaft and remove the secondary shaft lock out lever.
Then i would use #75-#76 main jets and CV, AU or CK secondary rods for better throttle respons.
HTH
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