Mercury 35/40HP 2 Cylinder Outboards Service Manual PN 90-42794--1, Page 56Get this manual
Main (High Speed) Jet Adjustment The carburetor is equipped with fixed high speed jet (a) and normally no adjustment is requiredHowever, extreme changes in weather (temperature and humidity) andor 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 enrichen the fuel mixture
Rejetting Carburetors for High Altitude Operation
The carburetor jet installed at the manufacturer is for engine operation at sea level through an elevation of 2500 feet (762m) above sea levelIf the engine is to be operated at an altitude higher than 2500 feet above sea level, it will be necessary to rejet (remove the carburetor jets and install jets with different orifice size) the carburetorsEach time the engine is to be operated at different elevation from the previous timerefer to theCarburetor Jet Charts," followingand rejet the carburetors for elevation engine will be operated at
Vent Jet