Just because you didn't install a fuel controller doesn't mean that the bike is running with a correct A/F ratio. And, just because you don't know of anyone that installed a M4 (or any other brand), that doesn't mean that the bikes are running a correct A/F ratio. Any time (with maybe the Akro setup being the exception.....maybe), you install a freer flowing exhaust, you are going to be running in a lean condition, to some degree. How lean, you don't know unless you have the bike tuned by someone that knows exactly what they are doing.