Try a Johnson/Evinrude \\”decarboniser/carb cleaner\\” treatment . Spray in in there when the engine is warm , the whole can , till it kills. Let if sit for an hour , then fire that mother up run it. Then change the plugs and run 2+4 fuel treatment in every tank, same thing as Sea foam , or stabil . (& try a new inline fuel bulb and fuel filter with fresh gas & tcw3 oil , sometimes that may do it )