I had a XS750 a few years ago I rebuilt to a very good condition, Yamaha still sold masses of spares for it at good prices. The starter motor made me an appointment to hospital. It refused to start on the starter so I kickstarted it. It didn’t kick back, it just started mid kick and so I continued through with the kick and over extended my knee. The first time it was excruciating pain, but it subsided after 10 minutes and I was able to pick myself up off the floor. I wen to the doctor and booked an appointment for an MRI scan which showed a slight tear in my cartilage. I had a cortisone injection in the knee - very painful! But I was back kicking a few weeks later.
Then, almost a year later the same happened and I over extended My knee again. This time same result, but I couldn’t bend my knee or walk properly for a long time. I went to the doctor and was referred to an orthopaedic surgeon this time and he went for a cartilage operation< I had managed to cut off a piece of cartilage internally. He cleaned out my knee and all was well once more. Even better was that I was now able to fully close my knee and straighten it out when for many years it never worked fully.
I decided it was time to sell the XS and I advertised it on EBay, describing how the starter wouldn’t always work and that it wouldn’t idle when cold. When the winning bidder arrived to pay and collect it, I showed him how it wouldn’t start from cold. However, the starter did indeed fire it up, it also idled when cold on the cold setting of the choke, and then idled on the second setting, and then with it all off.
it never did that for me, perhaps it just wanted shot of me? The old fella buying it was overjoyed that it was better than I described it and added £50 for my honesty.