I had a motorbike that I could have explosions and yellow & blue flames out the exhaust. Enjoyed it greatly as a noisemaker.
Fire out the exhaust is not so good as that fuel is not being burned in the engine. So you should notice a power decrease when exhaust flames are present. xplosiions in the exhaust are called afterburning and are most commonly evidenced by a popping sound in the exhaust. This is commonly taken to mean that the fuel /air mixture needs adjusting.