Holley stumble trouble

[Bewy]

What size is the IFR? I would think it needs to be about 0.038- 0.040", possibly bigger.
Contrary to popular belief, if the IFRs are smaller than above, enlarging them will NOT make the idle richer. If the t/blade position is correct relative to the T-slots, the idle mixture gets adjusted with the mixture screws. Enlarging the IFRs will richen the T slot cct to help with off idle tip in. I am not sure if QF uses a restrictor/restriction to the T slot; often called the IDC, idle down channel, it supplies mixed fuel + air [ volume ] to the T slot. It may also need enlarging, & I would enlarge a minimum of 0.005".
Two other things you could try. A smaller IAB. That will help the idle cct activated higher into the rpm range. A smaller MAB will bring in the mains system sooner to pick up from the idle system tapering off.

 

[DrCharles]

Apologies for the hijack, but this info may be useful to OP and others struggling with driveability and AFR issues

I have been through all those changes, including installing TSRs
Dialing in my 950

If my t-slot comes in earlier or richer, it's too rich at the top of the t-slot due to the increasing signal (rising vacuum). And most low-speed cruising is on the slot, so a relatively lean AFR is desirable there to keep the plugs clean and get (half-)decent fuel economy. Similarly, cruising on the mains (60 mph/3000 rpm/15"Hg) also has a relatively large contribution from the t-slot due to the small throttle opening required to maintain speed, and AFR there is 14.5-15.... pretty much the AFR is reasonable everywhere except at the very bottom of the t-slot.

I think the QF just has an inherent problem with t-slot position and length, compounded by a cam that is large for street use... someday maybe I'll go EFI instead!

 

[Rat Bastid]

Apologies for the hijack, but this info may be useful to OP and others struggling with driveability and AFR issues

I have been through all those changes, including installing TSRs
Dialing in my 950

If my t-slot comes in earlier or richer, it's too rich at the top of the t-slot due to the increasing signal (rising vacuum). And most low-speed cruising is on the slot, so a relatively lean AFR is desirable there to keep the plugs clean and get (half-)decent fuel economy. Similarly, cruising on the mains (60 mph/3000 rpm/15"Hg) also has a relatively large contribution from the t-slot due to the small throttle opening required to maintain speed, and AFR there is 14.5-15.... pretty much the AFR is reasonable everywhere except at the very bottom of the t-slot.

I think the QF just has an inherent problem with t-slot position and length, compounded by a cam that is large for street use... someday maybe I'll go EFI instead!

If it’s actually going lean where you think it is, add some emulsion in the middle of the stack. A bit more emulsion will make it richer sooner. It may actually need less emulsion though as it’s probably going rich first. Just my thoughts.