2005 SO Johnson 4 Stroke 9.9-15HP Outboards Service Manual, Page 108Get this manual
FUEL SYSTEM CARBURETOR OPERATION
Low-Mid speed
12345Piat jet Piat air jet Pilot outlet Bypass port #1 Pilot screw
y AIRFUEL +AIR (MIXTURE) "FUEL
As the throttle valve is opened gradually, air flowing through the throttle bore increases in proportion to the valve opening angleAt this time, because fuel mixture jets from the bypass port #2 and those upstream successively, the optimum mixture ratio (AF) is maintained, raising engine speed smoothly