Gemini supplied me with a 420 / 60T plate wheel and carrier, and I have recently been studying the link Stefan provided, which explains chain pitch etc.
But now I am a bit concerned because I have been looking at 420 chain on ebay and it never specifies it for anything bigger than a 160cc engine.
It makes me wonder if it is designed only for smaller engines and wonder whether our 200cc's will be too much for it?