Update and ending.
Drove the hour over to friends place this morning and to make a long story short he did indeed have fuel delivery issues which were caused by combination of dodgy petcock and sticky float and which were pretty much solved by the time I got there. Carb cleaner sprayed easily through jets and orifaces. No need to remove pilot so did not learn what size. Bike fired up. Sounded good. Left after an hour he still had valves to adjust and fluids (oil, transmission & primary chain) to change etc.
Reminded me why I did not buy that 2nd hand Triumph 500 back in 79
thanks all