Size of SU idle mixture screw
#1 Size of SU idle mixture screw
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.
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#2 Re: Size of SU idle mixture screw
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.
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.
1E75339 UberLynx D-Type; 1R27190 70 FHC; 1E78478; 2001 Vanden Plas
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#3 Re: Size of SU idle mixture screw
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.PeterCrespin wrote: ↑Tue Jan 15, 2019 12:34 pmCheck the specs for BA (British Association) screw threads. They look like 1 BA or 2BA.
Best thing to do is email or call Burlen and ask them. They will know and they will tell you.
Andrew.
881824, 1E21538. 889457. 1961 4.3l Mk2. 1975 XJS. 1962 MGB
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881824, 1E21538. 889457. 1961 4.3l Mk2. 1975 XJS. 1962 MGB
http://www.projectetype.com/index.php/the-blog.html
Adelaide, Australia
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#4 Re: Size of SU idle mixture screw
Being a real nit-picker , don't you mean a 3BA die ??
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#5 Re: Size of SU idle mixture screw
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.
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