Deane,
Dont Coast, use the blasted brakes to slow down, thats what you put those big rotors on there for.
Now in regard to your jetting, if its a 'lean' pop then go to a slightly smaller air corrector in the main circuit rather than the idle-reason being that regardless of you having closed the throttle that big cube unit of yours will actually pull the throttle blades partially open under engine braking conditions. Think about it, you cannot get that much air thru those 3 or 4 idle and transition orifices of 1mm dia each.
As Pat has mentioned that combo is going to try your patience to get setup correctly-dont make it harder for yourself by trying to make the carburettor into a brake caliper.
Have just done a quick check on your jet sizes etc, its a mile away from where I would start , will post later, gotta go earn a buck- monday morning here.
Jac Mac