The 3 circuit carbs are all real rich at part throttle. The only way around it is to either Block the 3rd circuit or drill and tap it and make your own " jets " or restrictions using a 10-32 set screw.
I've blocked the 3rd circuit and added a restriction to the idle transfer slot on 2 # 9375 Carbs and both performed MUCH better after the mods. One of them was used on 3 differant engines.
There wasnt much if any change in ET, but idle quality was much improved and during part throttle operation there was a HUGE difference.
No More Blackend Spark Plugs.