In answer to my own question,after many phone conversations and forum trawling,the answer did in fact turn out to be the ICU.Now i didn"t discover this, it was in fact a brilliant guy called Stephen at Yamaha UK tech services dept.He spent ages trying to track down the answer so if any of you have a question,give him a bell.I"ve managed to source a used Brit spec ICU which hopefully should be here soon,so as soon as that comes and I get my cylinder head de-carbonised, I2ll be out playing in the sun again.If for any strange reason, anyone wants a restricted ICU let me know.