Motorcycle Repair: backfiring, combustion gasses, kawasaki vulcan

Question
My motorcycle is a 1988 kawasaki vulcan 1500se with 10,000 miles on it.  Recently I put Jardine aftermarket exhaust on it.  That is the only modification that has been done to it.  My question is since I put the exhaust on it, it seems to be backfiring more.  It backfires everytime you back off the throttle and it does it until you pull in the clutch or are almost stopped.  It even does it sometimes when shifting between gears.   THANK YOU  

Answer
The exhaust system you have installed is much less restrictive than stock, thus allowing improved exhaust scavaging. So more of the combustion gasses are drawn out the exhaust valves on the exhaust stroke. These gasses contain a lot of unburned fuel due to the stock lean jetting of your carbs. The resulting exhaust gas with unburned fuel vapor will ignite in the exhaust pipes. The carbs will require a rejett to richen them up, promoting more effecient combustion in the cylinder and less unburned fuel vapor being scavenged into your pipes. A rejett kit is most likely available thru Factory Jet Kits or Dyna Jet. I hope this helps thanks for asking

Randy