lambretta gori exhaust gear ratio

After some advice....
I have a TS1 236 in a series 2, run it on the dyno and the performance seemed ok, 21 bhp, 78mph top speed, plenty for me and I was happy with that...
However, in reality once on the open road, headwind, lardy arse sat on it....not performing at all, so ive had a chat to a friend who has suggested changing the gear ratios...
my question is , TS1 236, amal carb (I know throw it away) but its spot on, Gori 50m exhaust....
To cruise about 60 - 65mph what would be a good gear set up.
Pulls like a train 1st, 2nd & 3rd...then 4th gear is like....nothing there...engine revs drop, speed non existant
Thanks in advance for any assistance.
Trevor
I have a TS1 236 in a series 2, run it on the dyno and the performance seemed ok, 21 bhp, 78mph top speed, plenty for me and I was happy with that...
However, in reality once on the open road, headwind, lardy arse sat on it....not performing at all, so ive had a chat to a friend who has suggested changing the gear ratios...
my question is , TS1 236, amal carb (I know throw it away) but its spot on, Gori 50m exhaust....
To cruise about 60 - 65mph what would be a good gear set up.
Pulls like a train 1st, 2nd & 3rd...then 4th gear is like....nothing there...engine revs drop, speed non existant
Thanks in advance for any assistance.
Trevor