Richard - thanks. I'm in Channel Islands (where the cost of living is twice that of UK - average cost of a 3 bed house here is £500k)
I've seen the video referred to. My return is a lot less than that. Spluttery of course, but just a dribble as opposed to an interrupted flow. Maybe I'm being over cautious as I'm not familiar with BSA A series. It's a bike I've had in the shed for 30 yrs. origimally bought as a frame for an engine I was developing, but I decided it was too good (read complete) to scrap and renovated it this year. Engine was clearly high mileage with several signs of incompetent 'repairs' over the years but I think I got them all.
As said, I'm a bit worried as the return (no wet sumping so return = flow) is way less than my other bikes, either current or previous - and they're rollerbearing not plain, so can manage with less oil. OK, so I never knew the flow on my japanese or Weslake, but one could guess it by consumption.