Motorcycle exhaust popping is bad as it's an indication of either a timing issue or bad spark plug or the carburetor being out of adjustment and allowing too much fuel to enter the combustion chamber.
Popping on deceleration is due to unburnt fuel being ignited in the exhaust.
The reason you do not hear this on a bike with a stock exhaust is due to the baffling of the stock exhaust.
It is not only much quieter but also does not allow the fresh air to enter the exhaust due to reversion.
A motorcycle will shoot flames out the exhaust when the engine ignition timing is off and the fuel is not burning properly.
Either your motorcycle is getting too much fuel or the timing is off on the engine causing the engine to not burn the fuel correctly which leaves unburnt fuel in the combustion chamber of the engine.
Motorcycle backfire is something that happens when a motorcycle engine gets too much fuel or air.
Bikes or motorcycles come setup so that the carburetor (or fuel injection system on modern bikes) provides the correct ratio of fuel and air, to allow the bike to run at its best.
Excessively lean carburetor settings can contribute to backfiring.
If the mixture is too lean, it may burn very slowly and unevenly.
This condition, in turn, may result in burning mixture remaining in the cylinder until the beginning of the next intake stroke when it can ignite the incoming air/fuel mixture.
The exhaust popping sound from a motorcycle exhaust is caused by excess fuel being ignited in the exhaust pipes.
The excess fuel is usually a result of an incorrect air fuel mixture in your engine.
Next time you hear that noise, no need to worry your engine is not going to blow up.
Backfiring from a motorcycle is also a common sign of bad spark plugs.
If you're hearing random loud pops coming out of your motorcycle exhaust, then you have a backfiring problem.