The engine I bought on Ebay recently has responded to a couple of hours of cleaning and oiling.
Tonight I managed to get it to run for about three minutes on a burner from an oil lamp and meths. It seemed to be very happy until I started to alter settings (we all do it don't we).
I haven't managed to repeat it yet but I think I know what direction to go in now.
The 'original engine sounds' referred to in the available literature consists of a whistle which can be adjusted by screwing it in and out to give different tones so produced a 'chuffing' sound which is more like a hot fog noise than an engine noise.
Thanks to Nick H and Dave for their encouragement.