Shhhh, The Police Like It Quiet.

I have the MSA PREMIUM EXHAUST KIT installed on my 1972 240z which has a Schneider 274F Camshaft. I used to have the MSA TWICE PIPES set up and it never caused any deceleration backfire popping. Now with this one whenever i reléase the gas pedal on 2nd and 3rd gear i am experiencing a pop pop pop sound at the muffler. I even lower the mixture to 2.5 turns clockwise on both roundtop 3 screws SU Carbs and retarded the timing to 11 BTDC but it still been Heard. The kit i installed is the following:

http://www.thezstore.com/page/TZS/PROD/15-6302

and comes with an Xcelerator Turbo Muffler:

http://www.a-1performance.com/XLerator_mufflers/

This is the one i had before:

http://www.thezstore.com/page/TZS/PROD/spring02a/15-6031

Should i just consider replacing the muffler to some muffler that is more restrictive and has glasspacks?