Why is my motorcycle popping?

What causes backfiring or popping in the exhaust of a v-twin motorcycle engine?

• Answer:

  This is an over-simplification but here goes: In a combustion engine fuel and air mixture goes into the cylinder chamber, after which it is compressed by the "plunger" part of the cylinder that causes rotation in the crankshaft as it goes up and down. When the plunger is up deep inside the chamber, the sparkplug lets off a spark, causing the compressed fuel and air mixture to ignite and explode, sending the plunger part back down with great force... ...this process repeats over and over again causing rotation... After the explosion occurs inside the chamber, the burnt residue is ejected through an exhaust line. The timing here is very important and that's why engines are calibrated to open the fuel/air line, compress the plunger, ignite the spark, eject the burnt residue... So... As I understand it, backfiring occurs when the fuel/air mixture fails to ignite inside the chamber and is ejected out the exhaust line and is caused to explode there. For some reason this is more common during decceleration as opposed to acceleration. And I do not know what causes it to ignite inside the exhaust TO START OFF WITH YOU ARE CORRECT NOW. WHAT CAUSES THE ENGINE TO BACK FIRE DURING DECELERATION ESPECIALLY IN A V TWIN IS AIR. SOME MOTORCYCLES ARE EQUIPPED WITH AIR CUTOFF VALVES SUCH AS HONDA,YAMAHA,KAWASAKI,SUZUKI ETC. IF THE AIR CUT OFF VALVES WERE NOT PRESENT THERE WOULD BE ALOT MORE BACKFIRING DURING DECELERATION THE BACK FIRE DURING DECELERATION IS CAUSED BY THE UN BURNT FUEL THAT IS BRIEFLY SUCKED BACK INTO THE CYLIDER DURING EXHAUSAT OVERLAP WHEN THE EXHAUST AND INTAKE VALVES ARE OPEN AT BRIEFLY THE SAME TIME. NOW WHEN THE INTAKE AIR PLATE IS CLOSED SOMETIMES KNOWN AS THE BUTTERFLY AIR/OXYGEN CAN STILL BE SUCKED THROUGH THE PILOT AIR JET WHEN DECELERATING THE ENGINE BRIEFLY LOSES VACCUME THENSE SHUTTING THE AIR CUT OFF VALVE ON MOST CYCLES IF YOUR ENGINE IS IMPROPERLY TUNED THEN YOUR INTAKE AIR PLATE WILL BE OPEN MORE ON IDLE AND LET IN MORE AIR CAUSING BACKFIRING. MOST CYCLES WIL NOT BACKFIRE IF YOU PULL IN THE CLUTCH WHICH IS THE PROPER WAY TO DECELERATE ANYWAY. DECELERATING BY ENGINE BRAKING IS VERY DAMAGING TO THE ENGINE ESPECIALLY TIMING CHAINS IF EQUIPPED ALWAYS PULL IN THE CLUTCH WHEN COMING TO A STOP THIS WILL CAUSE LESS ENGINE DAMAGE USE YOUR BRAKES THEY ARE CHEAPER TO REPLACE THEN MAJOR ENGINE COMPONENTS. IF THE ENGINE IS BACKFIRING WHILE ACCELERATING YOU ARE PROBLABLY OUT OF TIME