Cliff's Quadrajet Parts and Rebuild Kits

Quadrajet Problem Solving => Diagnose a Quadrajet carburetor problem => Topic started by: 77cruiser on August 09, 2025, 02:21:35 PM

Title: Rich off idle stumble.
Post by: 77cruiser on August 09, 2025, 02:21:35 PM

I'm getting a stumble off idle light throttle tip in. I have the linkage in the outer hole, was worse on the inner hole.
Combo 421 SBC Vic JR. 227/239 @ 0.05 hyd roller 9.8 CR 18 deg initial w/10 deg manifold vac.
Pretty sure the accel discharge hasn't been opened up, I didn't note it on my sheet.

Title: Re: Rich off idle stumble.
Post by: Kenth on August 10, 2025, 12:40:19 AM

18 deg initial is a lot and to me it indicates a too lean idle circuit.

What carb and recipe?

Title: Re: Rich off idle stumble.
Post by: 77cruiser on August 10, 2025, 08:29:46 AM

17084226
Idle tube  .031
Idle down .052
Idle disc.  .093
IABP        .136
Idle AB moved to air horn .043
Lower idle bleed .062
MAB blocked drilled for Dual MAB .046
P jet   .074
P rod   52M
Inlet seat .144
Float 5/16
SAB .026
Hanger G
Rods   CV
Air valve 1.29

Goes rich at light tip in to about 10 AFR then back to 13-13.5

Title: Re: Rich off idle stumble.
Post by: novadude on August 11, 2025, 05:43:44 AM

Your idle calibration is similar to mine... I have .029" idle tubes, .043 UIAB in air horn, .062 LIAB, .046 IDCR.  Using .046" Dual MABs, and 74 jet w/ 54M rods.  Idle air bypass on mine is 0.089".   I have less cam (217/225 @ 0.050, 108 LSA).  I have 13 deg initial with ported vacuum advance (15 deg can).

I wonder if reducing the IDCR would help with the rich spike?