In this photo:
you can see the set screw (socket head), friction screw (knurled with spring) and travel limiting screw (slotted). I'm guessing that it's purpose is to limit the throttle rotation to opening the carbs fully and no more.
The last one was set at factory as restrictor for running in
You would not believe the amount of bikes bought to me to tune ( sometime the full monty) that were more than 5 years old and had never seen more than 3/4 throttle.
Bet some are still that way now
It also puts a nice dent in Le Mans tanks in a minor fall
Best plugged with short bolt IMHO, I don’t believe anyone has ever broken a throttle cable by stretching it with twistgrip, I’ve been trying for 42 years on a Guzzi, another few before that with Amal twistgrips