Hi there, there is only one place to get any Yamaha outboard tuned and that is Yampower in Glasgow, just do a google search and you will find them. Nobody is as good with Yams in the UK
i played around with a 40 twin, head skimmed, race reeds, simple clean of the ports, up one size on the mains and hotter plugs, it used to rev to just under 7k on the tiny tach, it ran 52mph on a zapcat with a 15p prop dead reliable as well