Hi Bastiaan...There were multiple versions of the WB30 ranging through prototype, pre production and production types.. Even an all alloy engine version....Mine was from the only full batch produced, for a Royal Navy Contract, and was the later type of bike..(100 machines in the contract)...

These varied in multiple ways from the prototype that you have posted a picture of...I've mailed you ref. the Burgess filter....Ian

email (option): ian@wright52.plus.com

Hi Ian its in the Technical section under Amal carburetters. One and 1/4 inch x 24TPI.

Regards
John

email (option): ukcarbsathotmail.com

Thanks John...That should have been the first stop....:flushed: ....Ian

email (option): ian@wright52.plus.com

Adapters are available from Hitchcock Motorcycles. So no need to make one.

https://accessories.hitchcocksmotorcycles.com/Amal-Carburettors/Air-Intake-Adapter/19215