Thanks for the replies.
Now having done a few more miles on my T100, I've decided to stick with the standard (18t) sprocket for the time being as it allows the bike to pull nicely 2 up loaded with luggage.
1st service later this week after which I'll fit the free flow air filter, bigger main jets(120's), 1 shim on the needles & remove the snorkel.
These mods follows Jenk's tuning advice but I won't be able to comment properly until the bike's done about 2k miles.
Nourton.