5 Reasons Why My Mower Won’t Turn Over Unless Spark Plug Is Out?

Mower owners may occasionally find that their mower engine will not start unless the spark plug is removed. But do you know why?

A defective spark plug, bad or dragging starter, improper valve adjustment, camshaft faults, or a damaged battery are the reasons why your mower won’t turn over while the spark plug is attached.

Continue reading to find out how to troubleshoot and fix your mower when the motor won’t start unless the spark plug is out.

Mower Won't Turn Over Unless Spark Plug Is Out

Why My Mower Won’t Turn Over Unless Spark Plug Is Out?

The most common reasons why your mower won’t turn over unless you remove the spark plug are:

  • Any issues with the Spark Plug such as improper installation, loose connection, faulty plug wire/leads, dirty or broken plug.
  • Mower Starter faults such as being sluggish, cable turning hotter, or not having enough power to start the engine.
  • If the Exhaust Valve is out of adjustment or the Valve won’t open.
  • Excess pressure due to Compression release broke on the Camshaft.
  • Faulty Battery.

How To Fix Your Mower That Won’t Turn Over with Spark Plug On?

When you notice that your mower is no longer turning over while the spark plug is still turned on, check the following likely areas for any faults and fix the damaged element.

1. Check the Spark Plug for Any Potential Problems

The first thing to check is whether the spark plug was properly installed.

Because if the spark plug is not properly positioned or has a loose connection issue, it will not produce enough sparks to start the engine when you turn on the ignition key or pull the starter rope.

Similarly, a dirty or broken spark plug will also fail to generate enough flame, and over time, if the plug wire/lead has worn out or turned bad, your mower will fail to start.

What to Do

Locate the spark plug on your mower, and if you are a beginner, you can get help from your mower’s user manual to locate it.

Remove the plug wire and inspect whether it is in good condition or replace the spark plug wire.

Also, use a digital multimeter to test the plug lead and if needed, replace the lead.

Then take the spark plug off your mower and inspect whether it’s corroded or covered with dirt. If that is the case, clean the spark plug.

But if it looks broken or severely damaged, test it with a multimeter to confirm and if required, replace the spark plug.

If the spark plug looks good, check the gapping and adjust the spark plug gap correctly.

2. Check the Starter to confirm it is in good working condition:

An old or deteriorated starter won’t have enough power to turn the engine and will keep dragging due to cracked magnets or bad brushes.

You might also notice that the starter cable gets too hot as soon as you try to start the motor due to a bad starter.

What to Do

Test the starter first to confirm whether it’s bad or still in a working state and to do that you will need:

A Battery booster/ Eliminator
A Source of 12 Volt
Jumper Cables

So, disassemble the starter and test the starter and if the test confirms that the starter is the problem, replace it.

But before you put the new starter on, add a little bit amount of Blue Loctite on the bolts that hold the starter in place.

If the starter seems good in shape, check whether it has a loose connection or not and tighten the bolts and cables that are connected to the starter to secure the connection.

Read Also: Lawn Mower Not Sparking: Reasons and Solutions

3. Inspect the Exhaust Valve for Potential Issues

If the exhaust valve on your mower is not adjusted correctly or has a clearance issue, the mower will also encounter a similar problem.

What to Do

Take the little valve cover off to get clear access.

You will notice that the cover has a seal wrapped around its internal side like that so make sure that seal is in good condition.

If the seal is damaged, put another fresh one before putting the cover on.

Find the top dead center of your mower engine, so that you can adjust the valve clearance.

To adjust the clearance, you will need:

A Feeler Gauge
A 10-millimeter Wrench
A t20 Bit
A Screwdriver

Then adjust the valve clearances according to the correct measurement.

After you finish adjusting the valve, put everything back together securely.

Still, Lawn Mower Won’t Turn Over Until the Spark Plug Is Out?

If your mower problem remains the same, try these…

4. Look for Broken Compression Release on the Camshaft

Generally, the compression release mechanism on the Camshaft of your mower will gradually wear off due to lack of maintenance, such as not changing the oil frequently or a broken spring inside the mechanism and the release arm falls inside the engine to cause such a commotion.

What to Do

If you have not changed the oil for a while, take the shaft cover off and check whether it looks all crusty on the bottom.

Make sure to clean all the rust out from the engine assembly and drain out all the old oil before adding fresh oil.

Remove the camshaft and check whether it has the compression release arm or the arm is missing.

If the compression release arm has fallen into the engine compartment, fish it out, and if the arm looks severely damaged, replace the entire camshaft.

5. Make sure the Battery is Not the Culprit

Any battery-related issue, such as a dead battery, loose battery terminals/links, or broken cable connections can also drive your mower to encounter this problem.

What to Do

Inspect all the battery terminals, links, and cable connections to ensure that they are in good shape and there is no loose end left causing improper connection.

If there’s any loose connection, tighten it to secure the connection and if you see any broken terminals or cables, replace them.

If you notice that the battery surrounding areas and terminals are covered with built-up rust corrosion around the battery terminals, clean them thoroughly.

Also, test the battery voltage with a multimeter and replace the battery if necessary.

Frequently Asked Questions (FAQs)

What is the ideal voltage for a lawn mower battery?

It should have a voltage between 6V and 12V, but 12 Voltage is the best.

When should I change the spark plug in my lawn mower?

You should either change it per season or after every twenty-five hours of use.

How often should I replace the camshaft on my lawn mower

A camshaft generally has the same lifespan as the mower engine so it will last just like the motor of your mower. But it is recommended to change the camshaft after every 100,000 or more miles of operation to be safe.

Your Turn

Various reasons can drive your riding or lawn mower not to turn over unless you take the spark plug out, and if you do not diagnose the issue promptly to find out the root of such a commotion, it can gradually cause further damage to your mower.

Therefore, as soon you notice this problem, check these 5 most common potential areas first and take necessary actions.

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