Hi Steve
Frist thing to do is to check that your ignition timing is right and the spark plugs are correctly gapped.
Then get the engine up to its normal operating temperature, connect a gas analyser to the exhaust. (if you can get your hands on one or a Gunson colour tuner will do)
The ajustment on the air flow meter mixture screw is turning it in (clockwise) richens the mixture and turning out (anticlockwise) will weaken the mixture.
If you still have the popping and banging from the exhaust then you may have a leak in one of the exhaust joints.
hope this helps you out a bit
Chris