5100s was discontined June 1st 2009 and was replaced with the 5105SC for 9 months then it was replaced with the 5105C March 1st of 2010. I've got one 5100S, five 5105SC and one 5105C The 5105C is the only one that has been cranked and used the other 6 are still new in their boxes and have never been cranked. I ran 93 octane ethanol free with Maxima full synthetic at 32 to 1 and never had any over heating or scoring. My first 5100S went back to Hamburg in 2010 for a tare down and analysis and they sent me a new 5105SC.It was the 5100 S. But it was always over 50cc. They slowed it down because of piston and bottom end failures from running too hot