Just flew my dad's 4*60 today. Was a pleasure to fly something you didn't have to be right on top of. The ST 60 pulls it very well. No reason why a 90 to 100 four stroke would n't do as well or better. He had flown it maybe three times before pulling the carb off the ST 60 to put on a ST2500. The plane then sat for over two years! Took me 45 minutes of alcohol and windex to get the cigarette tar off it. Just wish he had broken in the motor as it tends to quit easily.