The 4-storke OHV engine can provide 3500 Watts rated and 3850 Watts peak power. In full gas tank (4.5 Gallon) GT4000IO can last around 36 hours of continuous operating time in 25% load of generator.
The design of Fuel Tank Cap Air Ventknob is to prevent any fuel flowing to the carburetor area, making sure the engine cannot be turned on when not in use in any cases.