I had a Yamaha RS 125 in late 80's and did a lot of tuning up of the little engine, (125 was the limit on a provisional when I was a lad Kipax
) By tuning up I mean buy all the bit's and go silly with a file for a day or two.
The way we used to test the top speed was to go on the East Lancs rd ( dual carriageway ) and assume the best wind resistent riding position.(head on the tank looking right, left hand on the left fork, right hand on the throttle, Mate on big fast bike on your right to ensure you hit nothing,and confirm your speed, as this position means you see very little but get crucial extra 5mph.)
As I got to my top speed my mate dropped back, I wondered what the h*** he was doing,and for one stupid moment wondered if I had outrun him, when a capri 2.8 police car pulled up along side
I sat up and slowed down but ...
I have a speeding ticket for 103 mph to prove my little shed could beat the TON
The only speeding ticket I did not mind recieving..