By no means am I an expert but .......... 4 stroking refers to a 2 stroke running like a 4 stroke............ the reasons are many. Too rich is most likely the cause. Smokeless formula oil will only go smokeless if mixed properly ( citation needed on that ). And a heads up for ya, the cleaner your fuel the cleaner carb the cleaner your motor. Think of it this way, would you put your motor together with gunk and crap? bailing wire and bubble gum? AND expect it to run perfectly ? Again I am no expert with 2 or 4 cycle motors but the " clean " part is something I do understand and it CAN in some situations cure a lot of problems.