Happiness is A10 shaped - well, the frames anyway.
Put a new battery in the big vee and it's starting great again. Also wired 12V to the 6V coils from the starter circuit and moved the start button from by the headstock to beside the twist grip. Been meaning to do those jobs for a while. That way I can give a fraction throttle it sometimes (rarely) needs on start-up. As expected, had to fit a diode in the circuit to prevent the coils back-feeding to the starter.
Only issue now is the silencer sounds more like a firing squad. Always has done. I presume it's carbs, but loathe to fiddle with them. I started out with 2 x new Mikunis but, after months of pain trying to jet them I gave up, slung them and bought new Amal Mk2's. The Mikunis plus jets etc lost me around £800. Can't recall the cost of the Amals, but at least they work. Trouble is, though, they work very similarly to the Mikunis whereby changing one jet affects the others. Hence my allergy to fiddling with them.
I was of the opinion overrun back-firing was too rich a mixture, but if anything it's weak - have to leave the choke on for several minutes until the engine is warm. Just a wisp of throttle on the overrun cures most of it - can you get helmets with ear plugs??