Points gap

After many years asleep, my 398cc ABC has been re-assembled and is running, but not smoothly. Feels too advanced. Magneto is fine but I wonder if the points gap is wrong. What is the correct gap? Any other thoughts?
Alan

i set my cav magneto
at 12 th. the old motoring books say 12-14 th.

Hallo Alan,
Provided that the valves aren't sticking and that the valve timing is correct ("valves dancing at TDC on one cylinder or the other"), there's only Ignition and Carburation to consider
(1). Set the magneto to be fully retarded at TDC, and its points at 12-14 thou., after cleaning them. Set the 'plug gaps at 16 thou.
(2). Check for air leaks in the inlet manifold: inside the 'heating muff' (rusted through internally) and at the manifold-to-head joints.
Still no good? Report back!

Thanks both. The points were actually set at 16 thou - an old note in the docs I have from long ago, so I’ll correct that. Also definitely need to check all joints as you say. The manifold is in good condition with no internal rot as far as I can see. Could you just explain “dancing” ? Predictive text at work? Or a term I’m unfamiliar with….
It’s running but is not happy.

hi alan it is hard to know if the manifold is in good order as there are 2 skins and you cannot see the inside one. hot air goes between the 2 skins so if the outside is ok but the inside slightly rotten it will pull air through and weaken the mixture. take the hot air tubes off and stick blue tack in the manifold holes, that will block any air off, if there is a leak it should run better, you can always put them back latter. what jet have you in the carb. ?

Alan,
For a dancing lesson/explanation you are referred to the Forum column on VALVE TIMING, #982.