Scooterotica

I know the early S2's had the air box with the wider neck to allow more air to pass, but isn't it basically a S3 air box then? Or is there a subtle difference in diameters that I'm missing?

There's a post on here somewhere re TV2 airscoop/boxes in that the early TV2 (with the 23mm carb) had a larger unrestricted scoop and wider inlet to the airbox whereas the later TV2 (21mm carb) had a restricted and smaller inlet to the airbox..............if I recall the post correctly.

The big difference is the air filter. On the series 3 the air filter is fixed to the filter box elbow with the bolt and plate arrangement.
The elbow is then held onto the airbox by a large spring clip.

On the series 2 the filter just sits inside the box and is held in by a wingnut which also holds the elbow to the box.

Yes, you're right Ian. I had forgotten about that. I had vague ideas about swapping the restricted box for a S3, but then of course you'd have to change the elbow and by then you are beginning to lose the 2'ness of it.