Hello John, Sorry you wasted your time, No two vin's are the same, I think Tims special has very long inlet manifolds. I remember years ago a USA article on Ram Stacks, I think it works out if the length from the inlet valve to the end of the carb bellmouth on mk2 cams is 14 inches you get a mild supercharge. I wonder what your petrol is made of ??. Some time ago on the Forum, A bloke from AUS told us about special spark plugs that cost a lot and were very hard, I had to try them, What a pain that was, the silly thing was, The bike was fine before. Is that why we run these old bikes, Something to play with ??. All The Best, Bill.