Hyundai 1 inch Owner's Manual page 22

6) High Altitude Operation
At high altitude, the standard carburettor air-fuel mixture will be excessively
rich. Output power will decrease, and fuel consumption will increase. Air-fuel
mixture will also be very likely to make the spark plug dirty and make starting
difficult.
Engine performance can be improved by installing a main fuel jet of a smaller
diameter in the carburettor and readjusting the pilot screw. If you intend to
regularly use the water pump at altitudes greater than 1000m above sea level,
contact us regarding a carburettor modification.
Even with a suitable carburettor, engine horsepower will decrease by around
3.5% for each 300 meter increase in altitude. The effect of altitude on
horsepower will be greater than this if a carburettor modification is not made.
If a carburettor suitable to high altitude is equipped with an engine suitable
to a lower altitude, the lean air fuel mixture will lead to lower engine output
power, over-heating and serious damage.
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