97 1100 spirit backfiring

 i have had this bike for a couple of years, last year the custom pipes
were replaced with cobra slash cuts (dont know if this has anything to do
with the backfiring)and the air/fuel mixture set plugs are gone, probably
to set a jet kit when the previous pipes were installed.I changed the
plugs and air filter at the end of the season last year. I have put on
about 2000 km this year. then bout a week ago my 97 1100 spirit started
to backfire when decelerating, 1 or 2 times with each down shift at low
RPM's, just about the time to down shift again. lean mix according to
everything ive read. checked the mixture settings and found them to be
way out, 1 @ 3 turns and the other at 5. Set them both at 3.5, and
changed out the fuel filter for good luck. also added a can the carb
cleaner to the gas. not a fan of additives but what the hell. So now it
back fires now and then, not all that often but enough to bug me. has ne1
had this problem and found a fix. going to have to take it to the shop if
i cant fix it soon.
thx...

 
Lean mixture causes backfiring (piffle piffle snap) during
deceleration, but a rich idle mixture can cause rumbling (boom boom)
as excess fuel burns off in the exhaust.

3-1/2 to 5 turns out on the idle mixture screws sounds like a lot,
considering that your carbs probably have #42 idle jets.

Use 4 or 5 ounces of Berryman B12 Choke and Carburetor Cleaner in a
full tank of gasoline to clean the tiny ports and passages in the
carbs if the back fire goes piffle piffle snap.

Your carburetors have a small diaphragm built into the side which is
supposed to shut off idle air and reduce deceleration backfiring, you
can see them in the Carburetor Components diagram at

http://www.powersportspro.com/pages/parts/viewbybrand/default.aspx

The diaphragms seem to work well enough, usually all I hear is a few
farts as I slow down.