i have an answer for this .since all the cases are now 50 plus years old now,,this is what you do,,,with the quadrant in your hand,,gently grind off a small amount on the first tooth surface so it dosnt over engage into the chainwheel cog ,,just a small amount,,this is due to the wear in the starter shaft boss hole becoming slightly elongated,,,and and and when you kick the engine over, kick rearwards and down,,,not just downwards,,,,,cappiche?