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If your John Deere loses power when the blades are engaged, it may be as a result of loose or worn belt, faulty spark plug, bad safety switch, or clogged fuel filter.

In this article, I outline 13 common reasons, diagnoses and recommended fixes to the problem to get your John Deere riding mower working efficiently again.

Contents show

Reasons Why Your John Deere Riding Mower Loses Power When Blades Are Engaged

Some of the reasons why your zero-turn may lose power when blades are engaged may include:

Dull Blade
Worn out blade spindle bearings
Dirty carburetor
Clogged fuel filter/fuel lines
Blocked air filter
Dirty cooling fins
Loose/worn mower belt

Tools You May Need for This Job

Torque wrench spark plug socket
Work gloves.
Spark plug tool
Compressed Air
Wire brush

John Deere Riding Mower Loses Power When Blades Are Engaged: Possible Causes and Fixes

1. Dull Blade

When the blade is dull, it has to work harder to mow through the grass which can cause the mower engine to lose power when blades are engaged.

This will further affect the functionality and performance of your John Deere riding lawn mowing machine.

Diagnosis

Inspect the blades to see if they are dull.

Fix

Sharpen the mower blades or replace them if necessary.

2. Worn Out Blade Spindle Bearings

Worn-out blade spindle bearings can be a reason why your John Deere riding mower may lose power when blades are engaged.

The bearings enable the blades to freely spin on their axis. If it is worn out, it can cause friction and may make your mowing machine lose power.

Diagnosis

Examine if the blades can freely spin on their axis. If not, it means that the bearings in the blade spindles are worn out.

Fix

Replace worn-out blade spindle bearings.

3. Clogged Muffler

The function of the muffler is to expel the burned gas and other vapors. If it is blocked by grass, dirt and other debris, it can cause your mower to lose power.

Diagnosis

Check the muffler for debris, dirt and other fluids.
If you notice a colored smoke that comes out of your zero-turn mowing machine, then there is a high chance that the muffler is clogged.

Fix

Replace the clogged muffler with a new one.

4. Blocked Fuel Filter/Fuel Lines on The John Deere riding mower

Dirt and other substances that are left behind by old gas can clog the fuel lines of your mowing machine.

The restriction of fuel can cause your John Deere mower to lose power and this will affect its functionality.

This is why it is always important to replace your fuel filter every year when performing your routine maintenance tasks.

Diagnosis

Inspect for clogs in the fuel lines by starting and stopping the flow of fuel using the mower’s fuel shut-off valve that is located beneath the gas tank. You can also start and stop the fuel flow by crimping your fuel line. Make sure that the fuel flow is stopped
Take off the end furthest from the gas tank of one section of your fuel line and place it in a container.
Start flow to inspect for any blockages.
Make sure that you also continue to check other sections of the fuel line.

Fix

When you detect the blocked fuel line, take off the section of the line and spray a carburetor into the line to loosen up the clogs.
Blow compressed air through your line to eliminate the obstruction.
Replace the old fuel line with a new one if you cannot remove the blockage or you notice that the line is cracked or dry.

5. Bad Safety Switches

The function of the safety switch is to monitor the pressure on the seat and can shut off power to the blades if it senses that the seat is occupied.

When the safety switch gets faulty, it may cause your mowing machine to lose power and the blades are engaged. This can affect the functionality of your John Deere riding mower.

Diagnosis

Check for any fault in the safety switch. If faulty, it requires that you change the safety switch.

Fix

Replace the bad safety switch with a new one.

6. Old or Bad Gas

Using a bad gas that is contaminated with excess moisture may cause your riding mower to lose power.

The gas may contain some ingredients that may evaporate and leave gummy substances that can block the fuel system.

Diagnosis

Inspect your fuel system to confirm if there are sticky substances left behind by old gas. You need to drain your gas tank if you observe that the gas is more than 30 days in the gas tank

Fix

Ensure that you drain the old gas, flush the tank and add a fresh one. In addition, you can also add a fuel additive to your fuel system to stabilize your fuel against the accumulation of ethanol separation and moisture.

7. Dirty Carburetor

The carburetor can regulate the right amount of air and gas that should be allowed in the cylinder to form combustion.

Dirt and other substances left behind by old gas can cause the carburetor to be dirty. This will cause the mower to lose power when the blades are engaged.

Diagnosis

Check the carburetor for dirt and other substances left behind by the old gas.

Fix

Clean the carburetor or replace it if it is in bad condition.

8. Dirty Cooling Fins

The cooling fins of your John Deere riding mower are an important component that can help to circulate air around your mower engine and keep it cool.

The engine cooling fins can get clogged with grass clippings and mud inhibiting the amount of air that can push to your mower engine.

Diagnosis

Inspect the engine cooling fins for grass clippings and mud. If it is dirty, it indicates that you need to clean the debris.

Fix

Clean the debris that is around your engine cooling fins. If the fins are broken, you may need to replace them.

9. Dirty Underside

A dirty underside might be one of the reasons why your John Deere riding mower may lose power when the blades are engaged.

This issue is common with Husqvarna John Deere riding mowers. Whenever the blade is engaged, the underside rotates on a crankshaft to mow the grass.

The mower engine can shut off if there is an interference in this rotation.

Diagnosis

Inspect the connection of the crankshaft to see if it rotates freely. If the crankshaft’s connection does not rotate freely, it indicates that the mower’s underside is dirty.

Fix

Clean the blade so that it will be free of debris, dirt and grass.

10. Loose or Worn Mower Belt

When mower belts are not properly routed, they will cause issues when the blades are engaged.

In addition, a loose belt can also slip off the pulleys, causing the mower to lose power.

Diagnosis

Examine the belt for wear, cracks, breaks, or slippage.

Fix

Replace the belt if it is in a bad condition.

11. Bad Pulleys

The mower belt drives the pulleys, which in turn moves spindles.

If the pulleys cannot turn freely, they would cause the engine to lose power. This will affect the operation of your John Deere riding mower.

Diagnosis

Check pulleys if they are moving freely. If not, it indicates that the pulleys are bad.

Fix

Replace the pulley if it is sticky or damaged.

12. Blocked Air Filter

When you feel that the mower is losing power when it is operating, it is essential to check the air filter. A blocked air filter can cause power loss.

The engine of your mower needs air to operate and when it does not get the required air, it may run sluggish or stall.

Diagnosis

Take off the air filter from the air filter housing and check for dirt. If it is clogged, it means that you need to clean or replace it.

Fix

Clean the air filter or replace it if it is in bad condition.

13. Faulty Spark Plug

For air and gas to be ignited, the mower’s spark plug must be in a good condition and correctly adjusted.

Over time, it may wear out and it will no longer have enough power to ignite gas and air This can make the zero-turn tp lose power when blades are engaged.

Diagnosis

Use a socket wrench to remove the spark plug.
Clean the spark plug with a wire brush.
If the firing end is covered with carbon, it means that the spark plug needs to be changed.

Fix

Replace the faulty spark plug with a new one.

How To Replace Spark Plug on Your John Deere Riding Mower

Here are some tips on how to change the spark plug on your John Deere riding lawn mower:

The first step to take is to gather the required tools such as torque wrench spark plug socket and spark plug tool.

Note: If your John Deere has a V-Twin engine, it will come with two spark plugs.

Remove the spark plug wires, use the spark plug socket and turn the spark plug counterclockwise to loosen and remove it.
Remove the fouled spark plug and bring out the new one. It is possible that the new spark plug may not be set to the engine’s recommended size. In this case, check your owner manual to know the recommended gap size.
Set the recommended gap and gently bend it on the other electrode, check the gap and ensure that it is properly set.
Tighten the new spark plugs and check the specifications that are noted in the manual. Ensure that you do not over-tighten the spark plug.
Re-attach the spark plug wires.

Note: If your spark plug fouls regularly, seek the help of a John Deere technician to check the engine.

Conclusion

It is important to note that this is one of the most common John Deere mower problems. Some of the possible reasons why your John Deere riding mower may lose power when the blades are engaged include dirty cooling fins, bad gas, faulty spark plug, worn mower belt, and dirty carburetor.

I have outlined and explained the causes of these issues and practical fixes to identify and solve each of them.

If the problem persists after implementing the tips shared here, it is advisable to contact a technician for assistance.