1981-1984 Official Honda ATC250R Shop Manual, Page 226Get this manual
'83 ATC250R ADDENDUM
AIR CLEANER CASE
Remove the seatrear fenderRemove the air cleaner coverRemove the air cleaner element
AIR CLEANER ELEMENT
ELEMENT HOLDER
AIR CLEANER CASE
HIGH ALTITUDE ADJUSTMENT
The carburetor must be adjusted for high altitude riding (above 5,000 feet; 11,500 m)High altitude carburetor adjustment is performed as follows: Turn the fuel valve OFFLoosen the carburetor drain screw to drain the carbu retorRemove the carburetorRemove the float chamberRemove the standard main jet and install the applicable high altitude main jetAlso adjust the air screw, according to the chartReinstall the float chamber and tighten the drain screwTurn the fuel valve ON and start the engineAdjust the idle speed with the throttle stop screw4,5006,500 feet 6,00010,000 feet No128 1Y, turns out