Why does my 2012 Honda CRF150R Muffler Pop and Shoot Flames in Deceleration?

When I rev up my bike the muffler pops and shoots flames in deceleration.

Four stroke engines do that. I'm guessing your muffler isn't much of a muffler. Maybe it's even straight through. Usually the baffles contain that and you don't hear it or see the flame.

Gas is too high octane for your location.