If you are like most homeowners who mow their own lawn, you will find that when you first start the lawn mower in the spring, it is much harder to start than during the rest of the mowing season. Frustrated, forget you’re not a teenager anymore and forcibly yanked the starter. You may be thinking “I wish I had an electric start lawnmower”. If you have an electric start lawnmower, you might be thinking, “Man, this thing has electric start, but it still sounds dead. Luckily I don’t have those manual start models.”
If you try to start the lawnmower for a few minutes, you may have tried a few with the throttle open, and then your “helpful” neighbor comes over and tells you that water may have entered the engine. So you might try starting a few times with the throttle open and the choke closed. If you have a manually activated machine, you may be considering an upcoming chiropractic bill and wondering if hiring a neighbor’s kid to mow your lawn isn’t a bad idea after all.
So why is it so hard to start an engine that has been sitting for six months? If you look at the spark plug under a microscope, you can find the problem. If you look at the tip of the spark plug with the naked eye, it may look fine, but if you replace the spark plug with a brand new, clean and dry spark plug, your lawnmower may start in seconds.
The key to the mystery is that in a machine stored outdoors, over time, microscopic things will happen to the surface of the spark plug’s ceramic insulator. With the cycle of temperature and relative humidity, day after day, over time, droplets will condense on the surface of the spark plug ceramic insulator and evaporate again. Each time these droplets form, they rearrange the tiny carbon particles deposited on the spark plug when the engine last ran. When you try to start the lawnmower, the growth of the droplets as they form pushes these particles together in the conductive path, ultimately providing an alternative path for current (through the surface of the ceramic insulator rather than through the spark gap).
Carbon particles cannot completely shorten the material, but they provide a path with a low enough resistance that no spark is generated, or the energy of the spark is very low and the charge in the cylinder will not ignite. After the engine has started, the burnt heat in the calendar will solve this problem within minutes, so when you start the engine again next week, it will start normally.
A simple solution to this startup problem is to replace the spark plug. Of course, if you want a cheaper solution that doesn’t have to go to the store, I’ve got one for you, and it comes in the form of a hot flame. Propane torches work best, but if you don’t have them, a butane lighter or gas stove burner will work. You see, the ceramic insulator around the center electrode of the spark plug is made of a specific material, and there’s a reason for that. When the ceramic gets hot enough, the surface properties of the material catalyze the combustion of carbon deposits. If your lawnmower hasn’t started yet, it hasn’t been “hot enough” yet.
To solve this problem, remove the spark plug from the lawnmower and prepare a clean hot flame (propane burner or butane lighter or gas burner on the stove). Holding the end of the spark plug that usually connects to the spark plug wire, insert the other end (the spark plug end) of the spark plug into the flame for a few seconds and turn the spark plug several times to heat the center electrode and around ceramic. It only takes a few seconds. After removing the spark plug from the flame, check the ceramic material around the center electrode.
You should notice that the ceramic insulation around the center electrode of the spark plug appears bright white, whereas previously it was off-white or gray. Now your spark plug is as good as new. Put it back in your lawnmower and enjoy how fast it growls!