4-strokes tend to smoke more than 2-strokes, partly because they have higher combustion temperatures and partly because the combustion is more complete.
If the combustion is more complete it should smoke less not more. My four strokes smoke as much or less than my two strokes, but then I don't use a plug that is too hot or mixtures that are too rich. IMO most four strokes smoke more than they should because the user is using a plug that is too hot for the prop and nitro percentage in use.