If you still have the air injection system, removing it with one of these kits will help. http://www.newspeedmaster.com/html/ai_removal_kit.html
Make sure the exhaust pipes are properly tightened, there is a torque table somewhere here in BA.com. If something has gotten loose in the exhaust system, air leaking in will cause increased popping.
These engines are designed to perform well, and that does lead to some degree of popping when you open up the breathing. Best to just tune the idle mixture for best idle speed and let it pop. It is possible to set the idle over rich to silence it, but it will cost you as the idle and transition circuits come back into play at high speeds and misadjusting the idle will cost you a bit of top speed as well as wasting fuel and fouling the plugs.

Let's hope there's intelligent life somewhere in space 'cause it's buggar all down here. -- Monte Python