2001-2002 Yamaha 50HP F50Z/T50Z Ouboard 4-stroke engines service manual, Page 18Get this manual
IIGeneral 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 suddenly