on my wife's 1300vtx motortrike, I installed a car muffler w/a 2 into 1 adapter before the muffler. bike now pops some on deceleration, I've already desmogged it and that helped some. ideas?? I know problem is probably backpressure, but how else to alleviate it without increasing noise. wife's previous trike was 750 shadow which sounded like sewing machine, so quiet.