Carburettor Spary Tube

This page â https://www.princeton.edu/ssp/65-cub-data/library/amalbritbike.pdf â lists only one needle for all 850s, this being the '4 ID-ring' needle '928/104 (4 rings)' https://andover-norton.co.uk/en/shop-details/17478 â however discussion over at AccessNorton 'established' that this needle was for use with the stepped spray tube and mutes in the peashooter silencers â https://www.accessnorton.com/NortonCommando/mkiia-850-carb-needle-bean-can-vs-peashooter.23436/ â but also that, quoting user L.A.B., 'All 850 carbs except perhaps for a few very early ones that left the factory before the change was implemented (see Bob [Rowley]'s second letter) had the 929/107 stepped spray tubes and 928/104 4-ID ring needles': https://www.accessnorton.com/NortonCommando/mkiia-850-carb-needle-bean-can-vs-peashooter.23436/page-3

If you follow that thread, it was also 'established' that, when mutes are not present in the silencers, 2 ID-ring needles and 'normal' spray tubes can be used. Otherwise, the most important thing that I learned from that discussion is to use 260 main jets for my MK2A â which has an RH10 head. I know that's a fairly round-about answer, but I'm not the fount of all knowledge, I can only hope that helps anyway!