strange engine issue from 900-1400 rpm

[swamp rat]

Remove the air cleaner (engine off) then pull one of the air fuel screws all the way out and take a can of carb cleaner with the spray nozzle and stick it in the hole till it bottoms out, open the chope plate and throttle plate and look down the carb, give the carb cleaner a couple short sprays and see of you can see any carb cleaner spraying into the venturi, if not the port is plugged, repeat in the other side.

I have had the crap fuel we get today gum up and clog idle fuel the ports after just sitting for a while, i can usually just give the ports a shot of cleaner and clear them out.

I agree you could have a vacuum leak but i think you are compensating for the lack of fuel thru the idle circuts by screwing the idle screw on the linkage in too much thus opening the throttle plates too much and pulling the mix from the off idle circut.