What jets are you running? Plug the rear power valve! If that helps, try plugging both and jet it square.
Have you checkedthe float levels? That will change main start up and richness for a given jet.
Let us know, Don

Thanks

I ended up using a 4150 metering block gasket & punched a hole in it for the IAB , the 4150 gasket blocks the intermediate circuit off , changed the accelerator pumps out to smaller ones also , this motor runs clean & screams through the rpm range , don't think i'll bother messing with the intermediate cicuit , will leave it blanked off.

Those tailpipes smell good , no overfueling & i can pull a chair up , obviously spark lead played a roll also ,will check for any lean issues when i get to the track.

on my 3 circuit 9375 it definetly runs better through low rpm with 25 shooters. Thought they were way to small when I bought the carb and went 35's sputtered all the way through first. ended up back at 25's on my old 542 they worked best too??
This is because the anullar discharge boosters rain fuel with a low signal so all that extra shot is unneeded.

IMO float level is very picky on these. Have you checked it? It might help some. Adjust it to the bottom of the sight hole, were it only has fuel come out if you rock the fender. Then turn it another 1/2 turn down.
I didn't read through all the posts so if these have been mentioned pay no attention.

also sounds like its idling on the primary/intermediate circuit. Back all the idle speed screw out all the way, turn the back idle speed screw in after it touches the cam 3/4 turn, now adjust the front to get proper idle.