The overall power of the gasoline engine decreases by about 3.5% for every 1000 feet of elevation above sea level due to lower air density at higher altitudes. This reduces the amount of air mixed with the fuel in the carburetor and affects the air-fuel ratio of the mixture. The only way to address this problem is by reducing the amount of fuel in the air-fuel mixture with a smaller carburetor main jet. The standard carburetor main jet is sufficient for altitudes below 3500 feet. Above 3500 feet high altitude problems such as hard starting, reduced power performance, increased fuel consumption, spark plug fouling and increased exhaust emissions might become noticeable. Consequently, you are advised to contact Champion Power Equipment for more information regarding parts and procedures for high altitude operation.