mine has popped while engine braking, and only spitted once at super low rpm. I have also taken all the crap out of my exhaust so it might have popped because of the decrease in back pressure. Another thing also is that a 650cc single cylinder motor is going to be wired and sluggy at low rpm just because of the design of it. My cbr600rr used to pop when engine braking and that had 4 cylinders. My buddies 07 rmz450 also pops. I have about 540miles on my 690smc. I have also done the wire mod.