My generator starts but not give 220 volts power

Check the voltage regulator and any fuses or breakers.

Check its AVR or carbinbbrushes

As you haven't mentioned the model name and the power of the generator . First of all your generator's engine is not running properly by properly I mean it's not running on the required RPM normally in gasoline engines the rpm is set on 3600 first of all you have to assure that engine is running smooth as you have mentioned that it runs rough that means you check your engine first like change the engine oil, check the air filter and the carburettor clean them if required, and than the spark plug, clean it and adjust the gap or replace it than check the fuel it should not be old enough as it looses it's octane value or there should not be any other content in the fuel fallen accidentally, check the fuel filter as well it should not be clogged after doing all this start the engine it should run absolute smooth. Now go on the generator side. You said it produces power in between, for a little time or so that means there is a disconnection somewhere this means due to the vibrations in the unit it gets connected and disconnected. Check all the wiring fuses coming out from the alternator up to the power out plug

Check the AVR circuit