2005-2011 Honda FourTrax Foreman TRX500 FE/FPE/FM/FPM/TM Service Manual, Page 136Get this manual
FUEL SYSTEM
HIGH ALTITUDE ADJUSTMENT
At high altitude, the standard carburetor air-fuel mixture will be too rich Periormance wi ll decrease, and fuel consumption will increaseA very rich mixture will also foul the spark plug and cause hard starting_ Operation at an altitude that differs from that at which this engine was certified, for extended periods of time, may increase emissionsHigh altitude performance can be improved by specific modifications to the carbu retorIf your customer always operates the ATV at altitudes above 6,500 feet (2,000 meters), you shou ld perform this carburetor modification
Even with carburetor modification, engine horsepower wi ll decrease about 3.5 for each 1,ODD-f oot (300-meter) ncrease in altitu deThe effect of altitude on horsepower il be great er than th is if no carburetor modification is madeThis engine, when operated al high altitude with Ihe carbu retor modifications for high altitude use, wil meet each emission standard throughout its usefu lifeThe high altitude carburetor adjustment is performed as follows: Remove the following: carburetor (page 6-6) floal chamber (page 6-7)