Hot start - not

Having had issues with cold and hot starting on my 650SS a couple of years ago (in fact virtually ever since I have owned it),I had the magneto rebuilt by a well-known mag man. Upon re-fitting, it started perfectly 1st kick- result! Then I felt my leg getting wet.... the petrol tank had sprung a leak. This started a saga lasting over 2 years, before I was once again in possession of a tank which would hold fuel, the Norton in the meantime languishing in a corner of the garage. Resurrected late last year, I used it over one weekend, when it would start normally 1st kick from cold, but would not from then on. No popping down to the shop then, as I would be pushing it home. The other day I rode to a friend's house nearby, and was there for a hour or so, but, upon leaving, despite many kicks it still would not fire. We removed the plugs, which did not appear wet. We then bumped it down his sloping drive, and after 3 or 4 revolutions it fired, picking up instantly cleanly on both cylinders, ticking over steadily. Once running, it always runs perfectly, for any amount of time, but once stopped, it needs to be completely cold before it will respond to the kick-start. I 'phoned the rebuilder, who was helpful, but suggested I check all settings very thoroughly to eliminate any other possible cause, before sending the mag back to him. I have checked the timing, points, plug gaps, tappet clearances, carb settings etc, and all seems good. It has a single carb, an 1 1/8th 389 monobloc, #3 slide, 105 needle jet, #25 pilot. Plugs are NGK, and have tried BP7ES and BP6ES, with 18 'thou gap, with no discernable effect. Plain non-suppressed plug caps. 4S cam, with 16 'thou valve clearances. I run it solely on Avgas 100 octane; no ethanol has been near this engine! Ignition advance 32 degrees, points gap 13 'thou. The points were a bit wider, about 16 'thou, and the plugs 22 'thou. Changing the settings made no difference.

The one thing that puzzled me was the fact that the plugs were not wet the other day, but on other occasions when this has happened, they have been, after a period of furious kicking.

Does anything jump off the page to any of you learned souls, as to what it may be, apart form the bl##din' obvious, the mag?!

Thank you in advance.

Ian