Got the original exhaust back on, and wow!
Why did the chap before ever decide to change it!!!!? The standard one is quiet on idle, and up to about 4 thousand revs at which point it just grunts slightly.
I'm sure aswell that it's pulling better with the original on - shame I didn't get it brake tested before and after, but I'm convinced

Seems to be running alright with the piper cam too....... which is nice

Cheers for you help / advice etc once again.
Ric.