Yamaha F100B F100C Outboards Factory Service Manual, Page 22Get this manual
GEN INFO
General information
Acceleration pump
The function of the acceleration pump is to ensure smooth acceleration by preventing the air-fuel mixture from becoming temporarily lean in case the throttle valve is opened suddenlyWhen the throttle valve is opened suddenly, large volume of air is introduced into the engineHowever, because fuel is heavier than air, it is not possible to supply the volume of fuel that is necessary for the large volume of air that has been introducedThus, because it is not possible to achieve the airfuel mixture that is required by the engine, bucking or hesitation resultsFor this reason, the acceleration pump temporarily increases the fuel volume in order to adjust the air-fuel mixture to ratio that is necessary for the engine in case the throttle valve is opened suddenlyOperation When the throttle is opened suddenly, diaphragm (via the link that is connected to the throttle lever) operates to pressurize the air in the dashpotThe pressurized air distributed to the carburetors by passing through the in-line, one-way valve that is connected to the carburetorsThe pressurized and distributed air then utilizes the passage of the main air jet to flow into the main nozzleThe pressure of the air helps suck fuel from the main jet, which increases the fuel in the main nozzle, and thus achieves fuel enrichment