Mower Won’t Turn Over Unless Spark Plug is Out: 6 Easy Fixes

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By Marvin Tucker

Farming Equipment

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When your lawn mower refuses to start, you will find countless culprits. Such a situation will make you scratch your head and end up confused. This does, however, become more limited when your mower doesn’t start until the spark plug is gone. This indicates a faulty plug, a bad battery, a problematic exhaust valve, or a damaged crankshaft.

If your mower doesn’t start with the spark plug on, we will help you solve this issue. In this blog, we will break down all the associated causes. Also, we will discuss possible and suitable fixes. So, read on!

Why your Mower Won’t Turn Over Unless the Spark Plug is Out?

Regardless of the engine model and type of mower you have, the spark plug is always a vital component. It contributes to igniting the air and fuel mixture inside the engine’s cylinder. However, the mower engine won’t start when the spark plug malfunctions.

Another major contributor to this issue is a  faulty starter containing frayed wires. Sometimes, the issue concerns a damaged battery or a dirty carburetor. Generally, determining this issue’s cause helps find the right solution.

1. Inspect the Spark Plug 

If you remove the plug and the engine turns over, then the problem lies in this component. The problem may be as simple as a poorly positioned plug. Also, there might be an issue with loose electrical connections inside the plug. So, not all problems are associated with a bad spark plug.

Also, the plug might appear burned or broken. In this case, you may spot cracks on its surface. Also, unlike its original light gray shade, a frayed plug will be almost black. Moreover, a disconnected or worn-out spark plug wire will make this part fail to make the necessary flames.

2. A Malfunctioning Starter 

You might not be familiar with a starting motor if you are new to the world of lawnmowers. It is an electric motor attached to the gas-powered engine’s crankcase. It contributes to the starting process of the engine by turning the flywheel.

This motor consists of a starter solenoid and a starter cable. The former is a simple switch that feeds the motor with energy, while the latter is connected to the battery. This way, this component provides the engine with energy.

The motor solenoids may be cracked or contain faulty brushes. Also, an overheated cable indicates a problem with the motor. If your mower model relies on an old starter rope, you will experience a similar starting failure. The rope or the recoil might have deteriorated over time and frequent use.

3. Check the Exhaust Valve 

Each gas-powered engine consists of two valves, one for intake and the other for exhaust. These valves should open and shut, respectively, when the engine cranks. If they fail to do this, there will be a stuck fume vacuum. Removing the spark plug is the only way to release these stuck fumes. Eventually, the lawn mower engine will start and turn over.

Improper positioning or tightening of the exhaust valve is to blame for this issue. Moreover, the only issue with this valve could be improper clearance and stuck buildup. Regardless of the cause, you must access the valve to see what is happening. So, remove the cover to have a visual image.

4. A Damaged Crankshaft

 In a two-stroke gas engine, a crankshaft functions as a link between the flywheel and the pistons. This component relies on the open and shut motion. With its two protrusions, the crankshaft boosts the circular movement of the pistons, flywheel, and fan belt.

But once one or both of the crankshaft’s protrusions are damaged, the regular motion of the component will be lost. Damage to this part happens due to general improper maintenance of the engine. Also, worn springs will eventually lead to malfunctions in the protrusions.

A malfunctioning crankcase is not always fixed by removing the spark plug, but it might sometimes happen. If you have one of the earlier engine models, there may be a connection between both components.

5. A Dead Battery

A malfunctioning lawn mower battery may lead to starting failure, which is solved by removing the plug. If you correctly diagnose the culprit, this part’s issues are not complex and easy to handle. Aside from the loss of charge, battery connections might be unclean or corroded.

Also, loose cable connections will result in a bad battery.

6. Take a Look at the Mower Deck 

The mowing deck of any mower should always rotate smoothly to facilitate even cutting. With frequent use and a lack of maintenance, grass clippings will jam this part and make it unable to rotate. This issue might increase the chances of experiencing this main engine problem.

How to Fix a Mower that Won’t Turn over unless the Spark Plug is out?

Fixing a lawn mower with a spark plug on board that won’t turn over seems complex. In many cases, replacing the spark plug alone won’t solve the issue. Other culprits cause this small component to malfunction.

So, it is up to you to detect these bad parts and fix them accordingly. If you do not have enough experience fixing the mechanical components of a lawn mower engine, you can always seek professional help.

1. Fix the Plug 

A misplaced spark plug can never generate sufficient sparks required for the ignition process. Fixing this issue is pretty simple, as you must locate and correct its position. You can read the user’s manual if you are unfamiliar with this procedure.

If the appearance is no longer normal, try the cleaning method. You can use a knife or a wire brush to scrape off corrosion or carbon buildup. Cleaning is often not an excellent solution, but it won’t hurt.

Lastly, you can get a new plug in the event of cracks or damage. You can declare your spark plug dead if you grab a multimeter and receive no response. Also, adjust the small spark plug gap to provide a proper distance between the plug’s central and ground electrodes. This adjustment may revive the plug.

2. Replace the Starter Motor 

The replacement procedure for a bad starter should be the last resort. It would help if you started by testing the solenoid starter. You can connect it with a jumper wire. If the test shows that the motor turns over, the starter is not functional.

As for the whole engine starter motor, you should check all the wiring surrounding it before buying a new replacement.

3. Correct the Valve Adjustment

If you ever encounter any issues with valve adjustments, you will always need a feeler gauge. This tool is also known as a thickness gauge. The metal tool will measure the gap between the valve clearances.

Ideally, the exhaust valve should be adjusted between 0.4 and 0.6 inches. If the measurements are far from this average, you will need them readjusted. This can be done with a socket wrench or, more specifically, a 10-millimeter wrench.

4. Make Repairs to the Crankshaft 

The crankshaft is a very powerful engine compartment. So, it takes a lot of overwork and negligence to see a critical problem in this part. However, if the crankshaft operates well when you take the plug out, you should consider servicing this mechanical part.

Start by replacing what is frayed. Also, consult with a certified dealer for the best course of action.

5. Repair or Replace the Battery 

The best approach to this problem is thoroughly inspecting all the battery terminals and connections. Start by cleaning its outer surface. Then remove any corrosion that has accumulated on its terminals and cables. This can be done by scraping or brushing.

Lastly, tightening loose connections and replacing damaged ones is suitable for maintaining a functional battery.

6. Fix the Mowing Deck 

If you experience mowing difficulty, you must stop the engine immediately. Then flip the machine to determine the cause of the jamming. It would be best to unclog the deck, but be careful when approaching the blades.

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