The spark plug installation was easy to moderately difficult. I first removed the choke control knob from the snow hood by pulling it straight up, and then removed the four finger twist bolts that attach the snow hood to the engine. I then found that I had to also remove the top bolts that hold the handle to the frame and the bolt that holds the snow chute to the handle so the handle could be pushed down slightly to allow removal of the snow hood. The bottom handle bolts do not have to be removed, just slightly loosened. Care must be taken when removing the snow hood so the rubber primer button hose and the key ignition wire are not broken or disconnected. The spark plug wire can then be removed from the spark plug with fingers or a pliers, and the spark plug removed (counterclockwise) with a 16mm (5/8" might work too) deep socket. Put some oil on the threads of the new spark plug (Champion RC12YC) and screw it in (clockwise), and then push the spark plug wire on the spark plug. Before reinstalling the snow hood I found it useful to practice installing the choke control knob on the choke stem. Now reinstall the snow hood with the four finger screws, making sure the primer hose and ignition wire are still connected. Next install the choke knob. I found it useful to use a flashlight beforehand to determine the position of the choke stem beneath the hole in the snow hood. Now refasten the handle with its two upper bolts and tighten the two lower bolts. Then install the snow chute bolt. It's now complete.