Just bought a ´73 RT1 360, which is what I had 30 yrs ago. I can only get this 360 to about 60mph. It starts and seems to run fine. I am sure I used to run my old bike up to about 80 mph. I am prepared to overhaul if necessary but what other improvements could I put on to up the overall performance. I would like to keep exhaust stock(as I hope to keep outwards appearance as original as new) but any suggestions to get me more kick for the cash would be appreciated.