P.Body I think that was a possibility. Because once I drilled them out just a tad bigger,
my idle screws started to finally have a bearing on A/F. Once I get another chance I’m going to lean it out just a little more and then set the idle a little higher and see if the problem is soloved. Hopefully that gets rid of the off idle stumble. I’ll keep the post informed of my finding. It could be a few days before I get back to it.

18 Initial is not enough. You can lean the idle circuit and turn the mixture screws all the way in, but unless you start to burn that mixture at the proper time you will get incomplete combustion of the fuel. Your idle vacuum is low, with low idle vacuum the fuel takes longer to burn because it doesn't vaporize as much of the fuel. For testing purposes lock out your timing to 36 degrees, see how it responds...

My Pro Systems 950 was dead nuts on going down the track but pig rich at idle, adjusting the idle screws didn't do anything, I sent it Thumpercarb, he only worked on the idle circuit...It's perfect now. 1/8 turn on the idle screws makes a diff now where before NOTHING did.

My feeling is that the carb base calibration isn’t set up for only 440” and a small cam(230@.050).

I’d guess the idle circuit was calibrated to be used on a motor combo that’s quite a bit “racier” than that.
In a nutshell....... it’s the wrong carb.

As an experiment, I’d see how it would work if it were functioning more like a carb with a 2-circuit idle.

First, I’d look under the carb at the rear throttle bores.
I’ve seen some of them have the tiny idle discharge ports under the transfer slots, in addition to the discharge ports fed by the mixture screws.
If it does have the extra tiny holes, try turning the rear mixture screws all the way in, and basically close the rear blades.
You’d also swap the rear idle air bleeds to something much smaller, like what you’d use for a hsab.
Again, this is only if the tiny discharge holes below the transfer slots are there.

If they aren’t there, then I’d run the rear mixture screws not quite all the way in.
Maybe leave them out about 1/8 turn.
I’d still run the rear blades at almost shut(to start).
Leave the air bleeds alone.

Now, almost all of the idle fuel will be supplied by the primary side, which should noticeably improve the mixture screw sensitivity on primary side.

Start with the rear blades basically closed, primary blades set to as far open as possible, based on the transfer slot exposure.

After getting the motor up to full temp...... then you can tweak the rear blades open more to adjust the idle speed higher if necessary.
Don’t adjust anything until you’re at full operating temp.

I’ve found that 2 corner idle carbs can still work very satisfactorily with the mixture screws out as far as 3 turns.
The range I like to see then in is 1-3 turns.

If you can’t achieve a satisfactory idle mixture by 3 turns, then add 1/16-1/8 turn at a time to the rear screws.

Having the rear transfer slots not showing(or very minimally showing), along with the mixture screws turned way in will also lean out the part throttle cruise.

Go down .002-.003 on the ifr's and lower em if they're up top where the usually are is shelf carbs.....

Thank you Dom. I will try these things once I get a chance. I haven’t touched the ifr. Maybe I should just go ahead and make my cam change to the 243@050 .600 on 108 now and see what that does. I do plan to replace this carb eventually. I just don’t currently have the funds.

Big is USUALLY better imo and the bigger cam will change the vacuum and characteristics of the car as well.........

Not to hijack but what did he do to it? My P S 950 acted the same way.

Moving them down below the float level made a big difference in reducing fluctuation in my set-up.

You’re not hikacking 👍. I am curious as well. I haven’t had a chance to get back at it as the weather has been rainy and cold and I don’t have a shop. My plan is to work on it more this weekend. From the above posts it appears I have some things I can try.
Pondering over this I’ve been thinking. My vacuum is lower than normal at 7”. It’s usualy around 10”. I plan to plug the back of the carburetor to see if that helps. Right now it goes to the power brake booster. And I’m curious if I could be losing vacuum from there? Or could it be a carb adjustment? It is steadily 7”. I’ve seen as much as 12” on the dyno with the dyno 850 carb.

My normal mods plus compensated for his horrible 6000+ feet of altitude....Fast is right about QF and some other carbs having piss holes below the t-slots on the secondary side so I plug em w/lead shot and start w/the primary and secondary blades showing to same amount of t-slot for starters then salt to taste.....