Starfire 66cc with 36t Sprocket. Motor stock except for expansion pipe. 43mph on hot days. When the outside temp is cooler add another 3mph.
In this video you can see me run wot with glance at speedo. From 8:55 to 9:40 or something....
‪A Ride On Motorized Bicycle‬‏ - YouTube
With a little timing adjustment and carb tuning, different head I have reached 48-49mph. But motor really vibrates like crazy so I just run it stock.
BTW..top speed is the same between expansion pipe or stock muffler. But snapper on bottom end with expansion pipe.