For those interested.....this is the Amal 47/022 carb fitted to some Dennis Z type mowers . I've found quite a bit of info. Some parts are still available through Burlen Engineering who I found extremely helpful.
I have extensive experience and knowledge of the infernal combustion engine from the smallest right up to marine cathedral engines (steam turbines too). If anyone has problems with old engines please get in touch. Can't guarantee I'll have the answer but I'll certainly give it thought.