Options to stop backfiring/popping?

Hi folks, I've got an 82 KZ550A with an unknown 4-1 exhaust on it, and the stock airbox/airfilter. It's always run a bit lean, causing a bit of popping on decleration. Up to now, I've been mostly country riding, so it was never a big problem, but now I'm using it in the big city, and it's annoying with all the stops and starts you deal with in town. I've done reading here, so I know that the pilot jets aren't replaceable. I've got the air screws down in the half to 1 turn area. One other thing: the muffler is the type that routes the exhaust in a "s" shape, rather than being straight through with fiberglass packing.My question is this: Can I possibly shim the inside of the exhaust/muffler to restrict the exhaust and add a bit of backpressure? Or alternately, could I possibly experiment with restricting the air filter a bit to richen the mixture a tad?
These are just some ideas I'm throwing out there. Any suggestions to help this low-end popping problem would be appreciated. I'm not worried about losing any performance gains that the 4-1 might have given the bike. I'm just trying to make it more civil.

1/2 turn of the air screw is not very much. You may need to go up one size on the main jet.

Going up on the main jet will not work. You are to lean in the idle circuit. Are you sure turning the pilot screw in richens it up or does it lean it out? What type of carbs are you running?

82 was about when the 550 cut over from an air screw to a pilot mixture screw so I can't swear which the fella will have. Increasing the size of the main jet will obviously not help because the backfiring occurs on decelleration; when the throttle is shut. This is the PILOT circuit. The thought about restricting the airflow into the air filter will mess up performance at all rpms.


OK why would a bike backfire?
1. lack of back pressure in a noisey exhaust
2. bike is equipped (like the 550) with an emissions system that dumps cold air into the exhaust runners to burn emissions via the reed valves
3. bike has leak in pilot system (orings on screws shot)
4. bike has leak in vacuum lines, fittings or vacuum plug allowing cold air into the combustion chamber
5. bike has bad / reused exhaust gaskets (again, air leaking into combustion chamber)
6. pilot/idle mixture lean (use larger pilots or adjust the air screw in or pilot mix screw out)
7. If you have clip slots on the jet needles, raise them one slot in conjunction with the adjusting the pilot mixture

I'm running the stock carbs, which are Tekei's(sp?).The problem with the Tekei's is that there are no optional size pilot jets. and yes, the screws should be turned inward to richen. I just discovered that two of the engine to carb boot clamps were loose. Tightened them up and took it for a ride. It helped a touch, but not much. I'll try turning the screws in a bit more tonight on the way home, and see what happens.
I was thinking restricting the exhaust would return the backpressure closer to a normal level. Sounds like a better idea than adjusting the carbs down to an unnatural level, but I'm no expert.
More opinions welcome!

Te 82 KZ550 A3 should still have TK-22 carbs. Those are the ones without the CV chambers on top.
On those, the mixture screw controls air only. Turn-in is richer. Turn out is leaner.

Like WG mentioned, look into blocking off the air-injection system. It causes a lot of back firing when it's broke, and it's not a necessary system to run the bike. Do a search, it's been covered many times.

Will do. Thanks for the replies. I didn't even think about the 550 having that air injection system, which is ironic, since I just got rid of the same thing on my'85 Ninja 900 a couple weeks ago. Duh!

Took off the air injection system this morning,and I just got back from a 50 mile ride. Didn't backfire or pop once! That was it! Thanks everyone!