I'd leave it be if it idles reasonable and doesn't die when let off the throttle - a little black puff is far better than lean - may need to have a talk with you dealer about fooling around with your tune - the vast majority know next to nothing about it other than just following the book

Since you just put the muffler on you really should adjust the pilot circuit.  It is easy to do.
After the engine is warmed up (at idle for 4-5 min)...

-start with the pilot adjusting screw at 1.5 turns out as a reference point, and count as you turn in and out so you always know where you are during the process.  Everything is done and referenced in the "# of turns out".
-turn idle up a little so you have a smooth fast idle
-turn pilot adjusting screw "in" until engine begins to slow downand note the # of turns out
-turn pilot adjusting screw "out" until engine begins to slow (it will speed up initially then go down) and note the # of turns out
-then set the pilot adjusting screw in the "Happy middle" of those two positions
-after the pilot circuit is happy, turn the idle adjusting screw back down for the idle you desire.

*for ex...if the turn in setting was at 1 turn out, and the turn out settig was 3 turns out, then the happy middle is 2 turns out.
**Turn slowly as you do this, no more than 1/8 or 1/4 turn at a time...then pause and wait 5 seconds or so in order to give the engine time to adjust, then turn again if necessary.  If you have a tach, then you can set the pilot adjusting screw by just tuning for max rpm, then set idle speed.
***If after you have finished this process, the pilot adjusting screw is 2.5 -3 turns out, then you definitely need the next larger pilot jet.  For myself, if I go over 2 turns out then I go up to the next size pilot jet.

When the pilot is properly adjusted, and assuming there are no exhaust leaks in the system, you will not have any backfiring.  It is normal to have some mild crackling and popping on brisk-hard deceleration, but there will not be any backfiring.

HAPPY TUNING  

LANCER wrote on 12/31/69 at 16:00:01:


Thanks Lancer - is the pilot adjusting screw the same as the idle mixture screw?  This is the screw that I can't get to move.  I scored the screw slightly when I drilled out the plug, but it was usable until the bike went to the dealer for its break in service.  Now that screw won't move.  I have a new one on order and if I can get the old one out I will follow your instructions on adjustment.

Jim_R - yea, I plan on a K&N, but like to make changes one at a time...get things right, ride for a few weeks, then make the next change.  I'm just slow about change that way.  I have a 55 pilot jet and a 155 main in the drawer if/when I need them...But if I'm rich at idle now - won't a 55 pilot jet make it worse?

Thanks everyone!

Do not bet all the eggs in the basket on one puff of smoke.  The best "at home" test is a full tune job as I described above.  Next to that, the absolute test is an exhaust analyzer which will show actual fuel/air mixture.  Be sure you have a new plug in it and go through the procedure...then check the plug as a follow up.
The pilot circuit is the primary fuel deliverer from idle to about 1/4 throttle, and regardless of speed or rpm, if the engine stumbles/backfires/whatever when in that throttle range then the pilot circuit is the likely culprit.                      

Performance international has K&N SU 6595 for $35.75 including shipping.

pgolden wrote on 12/31/69 at 16:00:01:


Thanks.  I called them to see if they had it in stock. I got a recording.  I'll try them Tuesday.

Steve

[ I've adjusted the idle mixture screw on my 97 and it really doesn't make the difference that lancer described, i.e ide speed doesn't change much.  I can only get about 3 turns, maybe 4, on that screw.  Is that normal?

I still get a pop on shut down and an occasional backfire when I drop the throttle.]


When turning the pilot adjusting screw there SHOULD  be a noticeable change.  As you turn it in, the engine should slow down to the point of stalling as you approach the "full in" position.  The same with turning it out, as you approach 3 or more turns out, it should slow again.  

If this is not happening then there is still a problem with clogged passages, or the adjusting screws are damaged, or you have an air leak between carb and engine, or some of the carb gaskets are damaged/worn so they are not sealing properly...there is something that is interfering with the tuning process.  I hate to say it, but you need to take the carb off and go through it  again.

By the way, the pilot adjusting screw is designed for only 3 turns out max.  Go beyond that and a larger pilot jet needs to be installed.  For many Mikuni carbs the "IDEAL" setting for the pilot adj scew is 1.5 turns out, with a range of 1-3.  When it is necessary to turn it out more than 3 turns  for best performance then a larger pilot jet is required.   Put in a larger jet and the adjustment will drop back down to the 1.5 +/- turns.If you have to turn it in to less than 1 turn, then a smaller jet is required.