Yes I have noticed 4 strokes tend to stumble less on transition. however most beginners cant or wont spring for a 4S engine on their trainer. Even used 4S engines command a premium price. These days I get all my used engines from my friend Bruce at brucercengines.com , he tests each used engine and gives them a rating so you know what you are getting. I help him do it from time to time, goes a lot quicker with two people.