Never seen that problem on a 4150, 4500 yes and that is fixed by richening the transfer slot jet and mixture screws. You could try turning the mixture screws out to richen in 1/8 turn increments til you get it balanced out between a clean transition and idle. Could be in the squirter or squiter pump cam also. Try whats easiest first.
The pump gas we have today don't help either. I sometimes have same problem in hot weather with straight pump gas. If I add some race fuel problem goes away.