I'm very familiar with those carbs, they are 1/2of a double pumper and great carbs.
If it ran good for quite some time and only began acting up after a fuel pump replacement then something affected something right then. A typical problem would be teflon tape used on the fittings or new rubber hose installed without washing it out so that trash has gotten to the needle & seat.
Except you say the float level was checked, hmmm
If it were powervalve being the wrong size that would've showed up when you first installed the carb, it has no affect on the idle unless it has gone bad and raw fuel is seeping past it and into the engine below the throttle blades.
Thats a rare possibility, a blown powervalve.
Did you have the carb apart prior to the problem. Did I restate the conditions right? it was fine untill the fuel pump change? Did the engine backfire thru the carb when the fuelpump failed?
