My BMW Petardea, why?

Hello, a month ago I bought an F-650 of 96, it has 50,000 km, I have used it to go to work and some small exit and it goes from cinema, but yesterday I could finally make a way out and after an hour APRX to a regime a little higher than normal notice any firecracker when reducing and cutting gas, the motorcycle was perfect and not notic This model in Spanish?

The firecrow is due to gasoline without burning that it comes out by the exhaust valve and runs into the very hot exhaust pipe.

This phenomenon is due either to a defective ignition (dirty spark plugs or in poor condition) or a poor carburation in mixture richness, or the accumulation of carbonilla residues in the butt and escape.

The carbon is precisely removed by circulating with the motorcycle giving cane, and when reaching higher than normal temperatures, it is when the explosions per exhaust occur when reducing.

The richness of the mixture is seen by carburation to the motorcycle, anyway a good way to know it is to put new spark plugs and circulate with the motorcycle at full gases for a minute or two, then stop the engine immediately without letting it turn to idle, you take out the spark plugs and they must have a light brown color, if they are too dark, the mixture has too much gasoline In gasoline. Both one thing and another make the motorcycle petardé.

The third probable cause is the ignition point and the state of the spark plugs, poor spark = no gasoline.

All the best.

Thanks for the Megabeat explanation.
I believe that the explanation that fits the most is that of the carbon, because when I bought the two covers of the motorcycle, they were practically square even to medium and I imagine that this indicates that the owner's antigo was very quiet with her, in addition if it was any of the other two explanations, I should petardear more often without it need to heat too much, right?
Greetings, thanks