Mike:
I automatically add Star Tron to every tank of Speedster gas year round, and add it to my yard machine gas cans year round, too - Even for the 2-stroke motors. Haven't had a single carb sludge up since I've been doing that, whereas I used to clean or need a new carb for something every couple of years.
With the Star Tron in there, I always add the clean-out, heavy dose amount to about a 1/4-ish tank in the spring or fall to clean things up for the new season. Both Speedster and yard stuff get it. I don't bother with the Sea Foam except as a season opener for whatever I'm dealing with, but I would not believe that it would hurt anything.