To set the story off right, I do have a moderate backfiring issue ( mostly when shifting from 1st to 2nd and when closing the throttle after holding it at 1/4 open for awhile).  So, I was out riding tonight and took a turn down a rather dark road.  That's when I started to see some flashes.  At first I thought that it was lightning and tried to race the storm home.  While standing at a traffic light, I held the throttle open about 1/4 and slammed it shut.  To my amazement, a solid blue flame shot from the tailpipe.  Is this normal for a backfire?  Is there a flame every time I backfire?   I know it's not good for the bike, but to tell the truth, it did look pretty neat.

The afterfire (commonly called backfire, but backfire is thru the carb) is caused by the epa tuned altra lean carb.  A pop upon closing throttle can be tuned out by readjusting the pilot screw on the right side of the carb.  The screw is hidden as it comes from the factory by a plug.  Most likely you'll have to drill it out to adjust it.  Give it about a 1/4 out (ccw), that fixed it for me.

Other sources of the pop are loose header bolts, torque them with the engine dead cold to 15 to 20 ft-lbs.

Or the slip on muffler clamp can be loose.

Also check the carb duct clamps, a leak thru there can cause it too.  

p.s. sorry about the late reply.  we must've been deep into another discussion.  Give us a shout if we don't reply.

The carb sits in two rubber tubes (ducts) that are clamped just like a water hose on a radiator. If the the one between the carb and the motor was loose enough you could possible suck enough air to lean out enough to cause problems. Should be able to snug the clamps up from the side of the motor.