1997+ Mercury 35/40HP 2 Cylinder Outboards Service Manual PN 90-826148R2, Page 153Get this manual
Main (High Speed) Jet Adjustment The carburetor has fixed high speed jetExtreme changes in weather (temperature and humidity) and or elevation may result in too lean or rich fuel mixture at wide-open-throttle, which may require change in the high speed jetA smaller size main jet will lean the fuel mixture, and larger size jet will enrich the fuel mixture