yeah it could be just a lot of mods that will be needed. ignition seems fine, locked out at 38. plugs are what you had recommended. I hadn't thought about hotter plugs.....
I’ll add that my buddies Pontiac Stocker idles just fine with the Qjet....... but it was a learning process on what it took t make it that way.
Lots of modifications to the low speed circuits.
He has a variety of carbs....... and on one of them we had to remove the primary metering rods to get any kind of throttle response from it(this seems to be pretty common with Stocker Qjets).
He now knows what series of things need to get plugged, what things need to get drilled, etc.......to get it to run right.
It took some time to get it figured out.
I’d think/expect it to be easier with a Holley.
Thinking about it more......
Even Holleys with “2 corner idle” have a secondary idle circuit, it’s just fixed instead of adjustable.
If the secondary idle circuit had been richened up too much...... that could be part of the problem.
You’re sure the ignition isn’t compromised, and you’re running hot enough plugs?
