The 'E' Type Forum

Hello. Does anyone know the size/pitch of the idle mixture (jet adjusting) screw on SU carbs. It appears to be a #6 but has an unusual thread count and I don't know if it's SAE or BSW. Burlen part number is WZX 981. Thanks.

Check the specs for BA (British Association) screw threads. They look like 1 BA or 2BA.

BA threads are used in electrical parts but maybe fuel too? There is also a thread family called BSF (British Standard Fine, which was used on British cars and bikes until the mid Sixties and there are the Cycle threads that are different again. With SU being such an old brand they could have chosen any of them for some historical reason.

PeterCrespin wrote: ↑

Tue Jan 15, 2019 12:34 pm

Check the specs for BA (British Association) screw threads. They look like 1 BA or 2BA.

I just ran a screw through a 3BA tap; perfect fit. If you want to check yours try the little circular thumb nuts that secure the instruments; they are 3BA as well.

Best thing to do is email or call Burlen and ask them. They will know and they will tell you.

abowie wrote: ↑

Wed Jan 16, 2019 12:34 am

I just ran a screw through a 3BA tap; perfect fit.

Being a real nit-picker , don't you mean a 3BA die ??

Thanks. I will try the instrument nuts. I did email Burlen but no reply yet. What an odd size screw but as Peter said, it is old technology.