Heads he wins
“I decided to drop a 400 top-end onto my 1980 Yamaha XS250. However I stuck with the original head so the compression was a little on the high side. On one occasion I broke a crankcase lug attempting to kickstart it. It was great road bike, although if held flat-out for too long the inlet valve would start to seize up.”
XS250/400 – a great road bike!