I took the bike to a local mechanic to adjust carbs as I knew they weren’t adjusted properly. The mechanic confirmed my suspicions and set the carbs up. As it was April in Scotland, temps were just above freezing, say 3 or 4C. There was snow on the hills - I remember that!
I was advised I might need to adjust the carbs come summer. Summer is here and generally we’re in the high teens centigrade. Which carb screw/s need adjusted?
In theory, yes, the mixture might need “leaning out” a tad to compensate for the lower number of oxygen molecules in a given volume of air in hotter conditions, but in practice a 15 to 20 degree temperature swing between seasons is pretty normal for the UK and shouldn’t need addressing mechanically. More importantly, how is the bike running?
Personally I doubt it’s necessary but if you feel like experimenting then it’s the smaller screw (to the left in the pic above) that regulates the mixture and, as all Guzzisti know, on a Dell’Orto carb it is an AIR screw rather than a FUEL screw, which means you open it (turn it anticlockwise) to let in more air and make the mixture leaner, and close it (turn it clockwise) to reduce the airflow and make the mixture richer. In your case you might try a up to a quarter-turn anticlockwise to see if this makes the bike run any better. Best do this after a run, with the engine fully warmed up.
The larger screw is the throttle stop, which controls the idle speed by raising and lowering the point at which the throttle slide rests in the carb body when the cable is slack. It is unlikely this will need adjusting unless your mixture is way out of whack. Turning it clockwise increases idle speed and anticlockwise reduces idle speed. Note that any adjustment to one carb needs to be mirrored on the other side (assuming they are set up correctly in the first place!), and that any change to the throttle stop screw setting will necessitate adjusting the throttle cable play and balancing it so that both slides move simultaneously off the stop when the throttle is twisted.
In short, you can spend hours messing about with carbs if you have the time and inclination, but as numerous previous threads will attest, not always with much to show for it. If all seems well and the bike is running OK it might be best to leave well alone!
The mixture screw controls fuel… screw it out and it will make it richer.. screw it in for leaner 
Thanks guys. I decided to leave the carbs alone as the bike, for the most part runs well. Thanks for the information. Much appreciated.
