Motorcycle Repair: yamaha 750 fuel, engine vacuum, intake tubes

Question
My Husband has a 1977 Yamaha 750. It idles very high when stopped. After adjusting the carbs it will work fine for a day or two. He is putting premium gas in it. Any suggestions please?

Answer
Shannon,

-I suspect the slides in the carbs may be sticking.
They have vacuum operated carb slides.
They rely on engine vacuum to open and have
a spring on the top to assist closing.
The springs may be weak or the slides sticky.

-Other causes could be idle set too high,
-Air leak around the carb intake tubes.
Spray some wd40 around the intake and see if
the motor changes speed.
-Check for sticky carb cables and or linkage.
-May need to clean the carbs and make sure
the float needle/valves are sealing ok.