Hot Start Problem

[33d6]

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.

[Rex]

Yep, always best to go "back to first principles" and check everything, especially when you see some of the dumbarse instant solutions on the Net.

[33d6]

I’ve been plodding through my early BSA literature. It’s made interesting reading. I hadn’t known BSA gave their ignition timings using full retard for several years. They came in line with standard practice sometime in the mid-30’s. They did a full turn around ferociously emphasising all magneto ignition timings were on full advance. In 1936, the last year of Mr Billingtons particular BSA ignition timing was now listed as 7/16” at full advance.
It was a similar curious story with the tappet settings. They were steadily increased over the life of that particular engine. Mr Billington is correct in saying the settings were inlet .004” and exhaust .006” in 1932 but had listed them as .004 for both the year before in 1931 and increased the exhaust setting to .008 for 1933-36.
Lots of food for thought there isn’t there.

[cardan]

That is interesting.

In particular the 0.004/0.004" valve clearances in 1931 seem very optimistic, very precise. I must admit that I don't use a feeler gauge at all on my vintage bikes, but just give them a jiggle to make sure they're ok. I reckon 4 thou on an exhaust valve wouldn't pass my jiggle test!

As for setting ignition timing using engine at TDC and mag on full retard, I do it all the time - it's my standard method on the side of the road. Easy to find TDC, easy to spot the points starting to open (in the BSA case open 3 thou - a quarter of the way to 12 thou). Done. Works every time. But, depending what has been done to the mag over the years, it sometimes means too much advance is available to the engine with the lever at full advance, so maybe the bike runs best on no-quite-full advance. Over-advanced ignition is bad. Not a problem for an experienced rider, but bad in the hands of a novice. Best to set the timing at full advance if you're at home in the shed.

Seriously, I wish Billington all the best with his bike, but he seems to misunderstand the BSA instructions yet stands by his misunderstanding even when others try to explain. I have done my best.

Cheers,

Leon