Troy, thanks for such formative info - that essay of yours really spells the YS history for me as for 4-stroke. One question, their is a 120AC and a 120FZ on ebay. Also their is a 120NC but in this particular auction, in the body of the description, the guy refers to this engine as an SC. Can you check this out on ebay and contact offline at: [email protected] and let me know your thoughts. question, would I be ok if I took the AC over the FZ - I'm really a balls-to-the-wall flier and speed is my game BUT I take care of my engines - thanks again for your info, Steve