My generator engine works fine but no electricity is going out!! But If I accelerate the gas with my hand it gives out electricity 100%!! What's the cause pleasseee?

Can it be the capacitor?

So, under load with speed up, it produces 120 volts? Not capacitor, could be regulator.

When I start the generator ,and plug a normal bulb it lights very dim very low and as I accelerate gas with my hand it lights properly!! My generator is 240v not 120v.Can you help please Thanks.

Try putting a heavy load on it. A light bulb may not be enough load to make the RPM go up.