Motorcycle Repair: Noise during downshifting, pop pop pop, motor escort

Question
Hi Chris.
I just bought my first bike - a 2002 750 ACE.  I noticed that when I downshift and roll off the throttle, a deep popping sound occurs... not a loud backfire... more like a slow throaty pop - - pop - - pop... as if maybe the engine is slightly misfiring.  As soon as I roll back on the throttle, the engine purrs as normal.  I added some carb cleaner the last time I filled up (with 97), in case the carbs were a little gunked up from being parked in a garage all winter.  But I filled up again yesterday, and the popping is still happening.  Is this normal during engine braking, or might there be a problem?
Thanks for your time & help.
-Anthony

Answer
Hi Anthony.

I had to smile a little when I read your question.
As a veteran motor escort officer, I had used that same method to help do a speed stop in that occupation.  When I did it with my girlfriend (who had never ridden a motorcycle before) on the back, she asked if I had engine trouble.

The popping sound is quite normal.  What happens when the engine revs increase is that the ignition timing advances a bit and retards when the rpms drop.  Engine braking causes an artificial advance of the timing, which opens the valves too soon and you get the popping from the cylinders.

Enjoy your ride.
Ride safe.
FALCON