Uhhh. Your gonna have to provide more info. At closed throttle on decel you are in the idle circuit. Try moving up to 45 pilots. Some gurgling on decel is normal- in fact, it is desired. Popping and backfiring is not. There is a brass part in the needle circuit It is sorta oval/round and goes between the mains and the needle jet, but that is only accessable from the bottoms of the carbs. The shim goes on the needle in the top of the carb. Shim/needle/chair/spring/lid. You are working in the top of the carb, aren't you? take a browse through this link at Pat's site...
http://www.dinqua.com/Triumph/Shim1.htmlI know those may sound like stupid responses, but I not sure where you are at in the process and I don't know the history of your bike or you knowledge/skill of carbs. Please be patient...
Phil's answer is right on for the tuning... I gotta know about those shims
