Cheers for the advice guys.. I realise it will be costly if I look at derestricting the bike. Re the power valves I'll check these again but I'm not sure they'll be wrong. As Tom had these set up by Fontty I think he said. The bike pulls really well, strongly and cleanly through the gears between say 7-10,000 rpm. But it seems to tail off at this point and changing up gives another strong 3,000 powerband and so on. Reading an old performance bikes mag in which there was an mc28 it also mentioned that the bike fell flat at the top of rev range.
So if there is anyone out there with a stock 40hp model i'm wondering if this symptom is normal or if by playing with the rc valves etc that I may see some improvement.