F5 are you aluding to what we call "knacking" where there are explosions in the pipe from unburned gases? My experience is it occurs as a result of overly rich low or mid speed jetting. It goes away as the revs climb when the engine clears out. Knacking is a random event. A steady event would not be knacking. Unless the original poster is just talking about typical 2T stuttering from running in an unloaded condition (part throttle).
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2011 EC250E
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