Join Date: May 2016
Location: Green Bay WI
Year/Make/Model: 2003 Vulcan VN1600 Classic
Color: Pearl Ivory
HA, great funny story. Must have been hard not to repeat that.
But, for the story, decel popping in the exhaust is not and never has been backfiring. Backfiring occurs when an ignition and or valve timing problem actually causes the spark in the cylinder to fire the air/fuel mix when the intake valve is still open and the power pulse burps backwards out the carb. That is backfiring which is extremely rare in these days of electronic ignition. The sure proof of decel popping is to pull in the clutch on decel and the popping immediately stops. The popping is caused by a very lean closed throttle fuel/air mix during decel. At idle a stationary bike can run without popping. But at speed on decel with a closed throttle the momentum of the bike continues to push the engine to pump, but it can't get enough fuel/air to support steady combustion. When the engine has turned enough to suck in just enough fuel/air for the spark plug to ignite the mix on the exhaust stroke, it "pops" out the exhaust.
Decel popping is just that, totally harmless popping. Because of lean fuel/air mixes on modern bikes, they all pop on decel. One reason the stock mufflers are so big and considered restrictive is to dampen exhaust noise enough to cancel out the decel popping. When you mod the stock exhaust (drill out the baffles or remove the baffles) the damping effect is gone and you hear the popping. Same can be said for free flowing aftermarket exhaust, most are much smaller in volume than a stock muffler and cannot dampen the exhaust popping. Another fact is most "free flowing" exhaust causes the fuel/air mix to lean out more yet, and the popping actually increases. Two ways to stop the popping, 1) pull in the clutch, 2) richen up the fuel/air mix on small/closed throttle and the popping is gone.
I know this by experiment. I modded the exhaust on my BMW R1100RS, made my own freer flowing internals inside the stock muffler. It popped like nuts because the freer flowing internals did not dampen out the exhaust. I had also installed a Techlusion fuel tuning system, and I could tune out the popping by richening up the fuel/air mix, and the popping was gone, along with about 5 mpg fuel economy.
Last edited by andyvh1959; 06-09-2016 at 07:44 PM.