Seafoam is of limited benefit for 4 stroke engines. It was originally developed for 2 stroke outboard motors.
Use a fuel system cleaner that contains PEA. I prefer Gumout or Techron. Both work well, are available at Walmart. Pick the cheapest. Either will remove fuel system varnish and deposits as well as clean up the valve stems and combustion chambers of carbon. Don't overdose. Follow the directions and be prepared to change engine oil after 10-20 hours of operation due to carbon soot in the oil. Thereafter, quality engine oil should be used to help keep the engine clean. Your fuel filter may need a change after treatment. While your engine is water cooled (I believe), I run Mobil1 5w-30 in my B&S Vtek twin. Synthetic engine oil in these smaller engines provides measurable benefits. Don't overlook valve lash adjustments...keeping the lash in spec can improve cold starts, improve engine power and help the engine run cooler. Also, clean and gap the sparkplugs. I always run plug gaps a little tight (0.003"-0.005" under spec)...helps cold starts.