What Does The Red Button On Your Lawn Mower Do?

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If you've ever had to mow a lawn or to perform lawn mower maintenance, you may have noticed a small, soft red button on the mower. In case you're wondering what the button does, it's not a safety switch or a means of controlling power. It's actually a small rubber component that's connected to the mower's carburetor. Depending on your mower's model, you may see it right on the air filter housing or on the carburetor itself. That little red button is called the primer bulb, and it plays an important role when you start the mower. Its primary job is to help deliver fuel to the carburetor before you get the engine going.

When you press the primer bulb, it forces air out of the fuel system. When you stop pressing, the bulb creates a vacuum and pulls fuel from the tank into the carburetor. This process ensures there's enough gasoline for firing up the engine when the starter cord is pulled. Without it, the engine might have trouble starting or fail to start altogether. Many manufacturers recommend pressing that bulb around three times before starting the mower so there's enough fuel in the system.

Note that you don't always need to press the primer bulb on your mower. Primer bulbs are most helpful for starting a cold engine: If the mower has been sitting for a while (say, overnight), the fuel may have drained away from the carburetor or even evaporated. The primer bulb replenishes it so that you can start the engine easily. Likewise, if the fuel system was emptied or your mower ran out of gas, using the primer bulb refills the carburetor to ensure the engine runs.

If your lawn mower isn't starting easily, a few presses of the bulb can make a big difference. However, if you find that pressing the primer bulb doesn't work, or the button keeps getting stuck, it's possible that the bulb is worn out. In this case, you'll need to replace it. Fortunately, these bulbs are widely available and inexpensive. 

If you're shopping for a new primer bulb, note that there are two types: vented and non-vented (wet and dry). Vented bulbs, like these Mudder Primer Bulbs, have a tiny hole at the top, whereas the non-vented ones don't. Depending on your mower type, the hole may or may not be there. Choosing the right type of bulb for replacement is important for preventing lawn mower damage.

Not all mowers come with a primer bulb, so if you don't see one on your mower, don't worry. Many newer gas models use a choke system to prime the engine automatically, while electric mowers don't need this type of system at all. If you're in the market for a new mower, you should weigh the pros and cons of gas versus electric lawn mowers for your yard.