Got Spark? - Symptoms That Your Mower Needs New Spark Plugs

The job of a spark plug is to ignite the fuel and air mixture that the carburetor sends to an engine cylinder. The energy created from this combustion process is what powers your equipment. If the spark is weak, this process cannot happen effectively. Assuming that you don’t have an air or fuel issue, the following symptoms will let you know that a spark plug needs replaced.

Hard to Start

The most common symptom of a bad spark plug is that equipment is harder to start than normal. A mower with a pull cord may take several more pulls before the engine fires up. If your mower has a key start, it will simply fail to start.

In this case, the spark created by the spark plug is too weak to ignite the fuel and air mixture in the cylinder. Each time you attempt to start the engine more fuel is pushed into the cylinder. The more fuel present, the harder the engine will be to start.

If you continue to try and start the equipment without success, you will flood the engine. Then it won’t start until the excess fuel drains from the cylinder. The fastest way to fix this problem is to remove the spark plug to drain out the fuel. Check out the condition of the spark plug while it’s removed and replace it if necessary.

Poor Engine Performance

A bad spark plug often causes an engine cylinder to misfire or sound like it’s struggling. The engine might even stall out completely while you are mowing. You may also notice that it becomes increasingly more difficult to restart the mower each time that it dies.

This happens because the electrode gap is getting wider due to the increased temperature of the engine. A larger gap decreases or weakens the spark output. Eventually, you won’t be able to get the mower started at all.

Fuel Consumption

If it seems like your mower is consuming more gas than normal, it’s time to change the spark plug. With a poor spark, gasoline burns inefficiently or does not burn completely. This causes the mower’s fuel efficiency to suffer dramatically.

Also because the fuel is not burning fully, you might also smell gasoline as the mower is in operation.

Physical Appearance

If you have noticed the above symptoms, it’s time to actually look at the spark plugs to verify that they are the problem. It’s easy enough to remove them and check. There are visual indications that will tell you if one is bad.

You’ll need a spark plug removal tool and a gap tool to properly check the electrode gap. Remove one and look it over carefully.

Signs of a bad spark plug

chips or cracks in the white porcelain insulator part
rounded or pitted electrodes
black electrode
electrode gap is too wide

The first two signs don’t have a fix and require a new spark plug. If the spark plug is in good shape but the electrode end is black with carbon, you can clean it with a wire brush. Clean off electrodes that look wet with carburetor cleaner and allow them to dry before replacing. You can also adjust the gap between the electrodes to increase the spark according to the mower’s manufacturing requirements.

These simple things may fix your power issues. If they don’t and you are sure that it’s a spark issue, replace the spark plug. They are pretty inexpensive and will pay for themselves with the amount of gas you will save.

Once you know the signs of a bad spark plug, you’ll be more likely to spot the symptoms sooner. This skill comes in handy not only for diagnosing your lawnmower, but also your other small-engine equipment like weedeaters and leaf blowers.

One way to be sure that all of your lawn equipment is in tip-top shape is to check it over and perform maintenance at the beginning of each mowing season. This includes replacing the spark plugs because they are cheap and easy to replace. That is what we do and highly recommend you do too.