Motorcycle Repair: 1983 XT 550--4 stroke, exhaust pipes, adjustment screw

Question
My bike is running good except for some backfiring.  I've replaced the spark plug, air filter, gas filter, and cleaned the gas.  I was told the mixture may be a litte rich, but can't find the adjustment screw on the bottom of the carb (there aren't any screws on the bottom of the carb.  Can you help with any ideas?  

Answer
Mark,
 Typically the fuel/air ratio adjuster is at the intake end of the carb. right below the barrel.  Basic setting is 1 and 1/2 turns OUT from seated.  You may be getting some LIQUID fuel blow by which is making it's way into the exhaust pipes and then igniting.  This can be from a overfilling float bowl caused by either an improperly adjusted floats or a sticking needle valve.  Other then that you may be dealing w/ incorrect timing, check to be sure.

Mike