2003 Johnson ST 55 HP WRL 2 Stroke Commercial Service Manual, PN 5005483, Page 115Get this manual
FUEL SYSTEM CARBURETOR MIXTURE ADJUSTMENT
CARBURETOR MIXTURE ADJUSTMENT
IMPORTANT: The slow-speed mixture in this
carburetor is controlled by an adjustable needleMake reference mark on the carburetor body before you disturb the needle adjustment
Start the engine and run it in gear at idle speed for three minutesAllow it to reach normal operating temperatureIf the adjustment is too lean, the engine will sneeze and backfireDo the following procedure: Note the reference mark and turn the needle 18 revolution counterclockwiseWait 15 seconds after each adjustment and repeat this procedure until you reach the highest consistent RPM If the adjustment is too richthe engine will be rough and unsteadyDo the following procedure: Note the reference mark and turn the needle 18 revolution clockwiseWait 15 seconds after each adjustment and repeat this procedure until you reach the highest consistent RPMDo this for each carburetorTo test the adjustment, run engine near full throttle for three minutesReturn the engine to idle, in gearThe engine should maintain smooth idle RPM