I have a Douglas SV54 engine fitted with the same model carb, so have pulled the main jet out and produced the attached drawing. I also have a Trusty with Norton Big 4 engine and Amal 225 carb. The main jet is identical to that in the Douglas carb apart from the spanner hex on the Douglas carb is 7/16″ Whitworth, where the Norton is 3/8″ Whitworth.
I think you will be very lucky to find anyone willing to make this. Even if you do, deep pockets will be required!! Expect the cost to be well into 3 figures.

Anyway, hope the drawing helps and I will keep my eyes peeled for a donor carb. Autojumbles are the best place to find them (if any take place in these challenging times!!). Online auction sites are a last resort.

Thank you all.

Collectively your comments will help me either fix, replace or decide to sell or break my machine for parts.

I don’t want to give in but it may be the most sensible option given that the end game is to clear out an make downsizing possible.

Busman’s stunning drawing (thank you for the time and effort) means I can delve into the possibility of having one made and yes, charlie, it will have to be a rewarded favour from a hobbyist.

I will also try the company mentioned by Norton 1952 as an option

Lastly thanks to Trusty220, I would love to read your project and see how you dealt with this car but don’t know how to find it on the site. Help?