I had a Pro Turn 160 with a Yamaha engine. The mower was great. The Yamaha engine was junk. At 87 hours, I had had enough of that lemon. The dealer gave me a full refund allowance in trade for a Pro Turn 260 with a ZT740 engine. I am very happy with the Pro Turn 260.
Don’t buy any used or old stock with Yamaha power.
You shouldn’t be hitting rocks with any mower.