When you fit a Banshee carb, be sure to use the left-hand one with the enrichener (choke) knob. You also have to plug the hole in the side of the carburetor where the choke crossover tube was attached. Otherwise, you'll have a big air leak and the engine won't run well.
In other words, look at your pair of Banshee carbuetors. Only one carburetor has a choke lever on it. The other one (right hand side) has no choke. When starting the engine cold, it gets its extra boost of fuel from the left side carburetor via a rubber tube connecting the two carbs. Unless you plan on installing a jetski-type primer kit, you have to use the right-side Banshee carb on your Blaster or you won't have a choke.
Just FYI.