Bugger - the yamaha jet appears to be a #1.4, and the jet that I successfully pulled out of the horizontal cyl carb appears to be a #1.3 - which is proving impossible to find online in the UK. I've emailed Allens and Factory Pro to see if they can supply them (if Factory Pro can I'll probably get his Config 30 jet kit and needle jets - maybe the long-boy idle mixture screws too).
Edit: Naturally as soon as I post this I stumble into the actual shop part of the Allens website, and find it listed as a BS30/97 jet
