Thanks, John.
Further investigations make me think that although the pump may have come from a BSA, it is in fact a B&L with the adjuster dial on the end of the regulator needle. This needle has a blunt, squared, end, and does not actually have any regulating effect at all. Makes me think that it should have a longer taper.
I'm running modern two stroke oil in it, and despite the huge consumption of the stuff, the exhaust shows only very slight smoke. I will change to a straight 50; it's a good point that the oil is always cold, so a heavier oil would reduce consumption.
The final, compounding, detail is that the engine is a 500cc Barr and Stroud sleeve valve. I'd expect oil consumption to be higher than for a poppet valve engine, but it shouldn't be that much higher, and certainly shouldn't belch liquid oil out the exhaust. The only other sleeve valve engines about are Knight double sleeves in cars. These are not total loss of course, but are a more complex lubrication challenge, and their exhausts run dry.
Wear is almost non-existent in sleeve valves due to the huge wear surfaces, and the valve action which spreads the lubricant very effectively. RAF experience with Bristols (which use the same single sleeve design) gave something like 10,000 hours between overhaul, versus 1500 hours for poppet valved engines. I know the full history of my bike, and am confident that excess wear is not an issue.
Thanks for your help.
JFerg