Termignoni Exhaust on Yamaha R6 Breathes Fire [Video]
Now, this 2010 Yamaha YZF-R6 has a racing Termignoni carbon-sleeve exhaust, which is both short and certainly filters out less gas than the standard can on the bike. But such backfire during engine brake simply doesn't seem right.
It may be that the engine is getting too much fuel which has no time to burn and ignites on its way out. Backfiring is also bad for the valves, no matter how cool it may be. Probably everybody know a guy who knows a guy who has wrecked his engine while doing silly excessive backfiring at bike rallies...
Nevertheless, the Termignoni sounds very nice, not quite the best sound to hear at night in your neighborhood, obviously, but on a highway or track, that can would be awesome. Again, maybe some mapping adjustment would be a great idea, with the modified exhaust line and all.