How to check the engine?
Start the engine. Make sure it starts up without any problems. Shift into forward gear, try some power, shift into neutral, then shift into reverse and try some power again. Shifting should feel smooth and you should always feel the transition between neutral, and the forward and reverse gears. Check to see if idle power can be increased (to recharge the batteries). Check that the engine is cooling down (the engine should be blowing water from the exhaust).