Smoke residue is normal with any Force 2-stroke motor. Having said that, you can minimize the amount of smoke by making sure Carburetors are clean and properly adjusted and idle fuel mixture is set correctly. Also making sure the fuel recirculation system is working properly. Some folks also say the certain brands of 2-stoke oil are less smokey than others. I've experimented over the years to see if I could reduce the amount of smoke to what I perceive to be an acceptable level without much success.