<VV> Gargle on the overrun

[Padgett]

What causes an engine to burble through the exhaust when coasting down ? 
Gargle would not bother me except I seem to sense (cannot feel it) a very 
mild misfire on light throttle cruise. Goes away when you stand on it (as 
much as you can with a 110/PG). Coil is new, plugs (W8ACs) are gapped at 
.030 and have only a couple of hundred miles on them. Has new-appearing 
orange 8mm plug wires from Clarks, valves are at 1/4 turn from click (set 
warm). Idle now smooth. Timing at 12 degrees static. Running on 93 PON & 50 
jets.

Pertronic II has been suggested, is that worth while ?

Padgett