High idle would usually indicate an air leak to the carb.
I would advise you to check the rubber boot from head to carb for cracks etc, also check the diaphragm in the top of the carb, these do perish and crack in time.
If those appear to be in good condition and not causing an issue my next step would be to clean the carb and fuel tank thoroughly and to add an inline fuel filter at the same time.
Jumping into gear...
I wouldn't be to concerned about that until you have sorted the high idle issue. The high idle will cause the 'jump' into gears.
I would advise you to check the rubber boot from head to carb for cracks etc, also check the diaphragm in the top of the carb, these do perish and crack in time.
If those appear to be in good condition and not causing an issue my next step would be to clean the carb and fuel tank thoroughly and to add an inline fuel filter at the same time.
Jumping into gear...
I wouldn't be to concerned about that until you have sorted the high idle issue. The high idle will cause the 'jump' into gears.