Jon, you are discussing this problem with a group of Australians all of whom regard 25degreesC as merely balmy, not hot at all and who play with vintage and veteran machinery much older than yours. As a 1932 model pedantically your bike isn’t even vintage. You may have a hot start problem but warm weather and age of machinery are not the root cause of your woes. It lies elsewhere.
I have a practical guide to BSA from 1931 written by D W Munro of BSA and first published in 1948 by Pearson in front of me. In his chapter on servicing old models Mr Munro goes on at length about “The Importance of Correct Ignition Timing” for nigh on two pages, finishing off the second page with other possible causes being weak mixture, tight valve guides, burnt valves and insufficient exhaust tapped clearance.
It may be time to again look closely at all these matters.
