The owner stated that the employees will run the saw hard and with a dull chain. He said the fuel was 50:1, but it was old (the brake down up did not occur recently) so I dumped the gas (as he also recommended). Also, he just brought the power head, no B&C, so I can't check it, but it sounds like the likely cause. I recommended 40:1 to him about a year ago (after this saw failed), and he has been using 40:1. I also told him to use high octane, will have to check if he did that.
I think he just transferred the B&C to his 066, and then that started acting up on him, and he took that one to the shop and the 660 to me. If the repair for the 066 is not reasonable, that may also be coming my way. I know he got a quote on replacing the P&C on the 660. Don't know what they wanted, but he did not go for it (maybe they told him it was not worth it???).
I don't know why this site will not let me post my pic of the piston, it is not because of the size, but I resized it anyway and it still will not post.??? Will try again, but I wish I knew what was going on.
The owner is a real straight shooter, and I trust what he tells me, but he freely admits his employees don't have much respect for the equipment (specifically, the saws).
Since he stated they often use this saw for stumping, the dull chain theory makes a lot of sense. Thanks for the input, I appreciate it (but I will still vac test it, just to be sure).