First of all make sure that your generator is not operated in any closed environment. A well maintained liquid cooled generator can run even up to 40,000 hours before a maintenance is required.

Emission of black smoke is generally due to incomplete combustion of the fuel. First any air inlet restriction should be checked for any blockage. The air filter should also be cleared for any dust. Injector malfunction and incorrect engine timing can also be a common cause for black smoke. Generators that run on diesel require less maintenance and are fuel efficient. But they are more noisier and emits much smoke. These are also difficult to start during winter. Propane generators however have no such starting problems.