Trying hard to remember the sixties and referring to the BSA 650 twin I had as a "fuel cooled oil burner". Leaning the mixture too much made it run hot. If the ignition was too far retarded or too far advanced it ran hot, though retarded was worse, I think?
The Hilman Imp boiled dry every ten miles on the way from Edinburgh to Cornwall so we stopped in the middle of the Borders and re set the timing, using fence wire and the interior light bulb. The radiator cap could be removed after 100 miles engine still running!
Happy days.