Idle speed problems may be caused by vacuum leaks in the carburettors or intake system, the starter boxes ("chokes") being partially "on", or the fast idle screw riding on the fast idle cam. Another common cause is a dirty or stuck temperature compensator valve. Remove the compensator assembly from the carburettor and spray the back valve with cleaner or solvent. Do not try to remove or adjust the long thin bimetallic spring. If the valve still binds or will not seal tightly against its seat when held with finger pressure, replace the compensator unit.