Popping on decel is usually associated with a lean idle. Either too lean due to an air leak, leaner than stock idle jet or, most likely, too lean mixture setting.
If everything else is as it should be, then with the bike nice and warm, slowly turn the mixture screws in or out seeking the smoothest and fastest idle. Sometimes they do run best when they pop on decel. Too rich an idle mixture makes the transition muddy and flat, too lean can make it rough or notchy.
Never underestimate the laxative properties of motorcycling.