N15 cs carb. main jet

I recently acquired a N15 cs 1967, it has 2 concentric mark 1 carbs. On stripping I found that both main jets were 260, My manual says they should be 420. The only reference I can find on here is Piero who quoted his as 220 and none of the replies questioned this. Could someone please point me in the right direction. Phil

I’d go with a 220.

https://www.inoanorton.com/docs/TheNortonCarburetor.pdf

Upon diving into my files further, it says 220 with air cleaner, 240 without. Your 420 jet is for a monobloc.

I have Norton Publication (P106/P). This manual does not list your bike model directly, but for the 750 Scrambler with twin Amal Concentric Type 930 carbs, it lists carb data as:

Main Jet:
with air cleaner: 220
without air cleaner: 240

Pilot jet: 25 cc

Throttle slide: 3

Needle jet: 0.107

Needle position: central notch

I would say your bike's carb data should be closely similar, with 260 main jet being close. A main jet of 420 may? be a mis-print (should be 240?).

Slick

Note: Paul W chimed in while I wrote this .... I would agree a 420 would be appropriate for a single carb.

excellent help, many thanks to all. Phil