There are several things you have to keep in mind when you start swapping carbs. I always put in a gasket set so I start with a clean setup first. The diameter of the throat is pretty important. Too narrow and your engine wont put out all it can. Too big and it just bogs down (maybe, never had one too big). Would the needle on the second carb work in the first carb? Just a shot in the dark. What do you think Ralph?
Edwin