My Allen scythe has a villiers 11c engine, the one prior to the 25c.
Mine has a midget carb but the 25c has a Junior carb I believe.
The Allen manual explains setting the timing etc so it may help you with your machine.
Best regards Mick
The saying goes “a picture paints a thousand words” , so a photo would help us help you. I would guess that it would be a “twin lever” carb , from their very fist models until the end of twostroke engined production , they seemed to favour and specify this style of carb. Ones for the earlier V111C engines seem more plentiful , as they were also fitted to numerous motor cycles , the ones fitted to the later 24/25c are like hens teeth.
I have my doubts now that it’s not an Auto Culta looking at “Fifty years if garden machinery” as the main lump of the m/c was red. I have the roto box and will take pics of both the rotobox and the engine and post ASAP