2006-2014 Honda FourTrax ATV TRX250 EX TRX250X Service Manual, Page 102Get this manual
FUEL SYSTEM Start the engine and warm it upAdjust the idle speed at high altitude with the throttle stop screw to ensure proper high altitude operation
IDLE SPEED: 1,400 100 rpm (min-')
I NOTICE
When the carburetor has been modified for high altitude operation, the air-fuel mixture will be too lean for low altitude useOperation at altitudes below 5,000 ft(1,500 m) with modified carburetor may cause the engine overheat, resulting in serious engine damage and increased exhaust emissionsFor use at low altitudes, you should return the carburetor to original factory specificationsReplace the main jet with the standard main jet, and screw out the pilot screw the specified number of turns from the high altitude setting