Mower Bogs Down When Blades Are Engaged? (We Have a Few Fixes)

Dennis Howard
by Dennis Howard
Nothing is worse than when a lawnmower bogs down when the blades are engaged. This can happen due to a poor throttle assembly, among several other reasons. Follow along as we explore the several reasons and fixes for a lawnmower that is bogged down when the blades are engaged.

When your lawnmower fails to perform, it causes more complications than just a little frustration. Being unable to keep your lawn and landscape in tip-top shape can be a major problem for some homeowners. For many who use a riding mower, a mower that bogs down is more than a nuisance.

A mower that bogs down when the blades are engaged is a symptom of bigger problems with your mower. You may not have a large enough mower if your grass is exceptionally thick or tall. Mechanical issues with the mower deck, drive train, or throttle assembly may also be to blame.

Diagnosing a problem with your riding lawnmower takes a bit of time and effort. By following a few steps, you may find the problem easily. The chances are, once you identify the problem, it is easily fixable.

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Troubleshooting a Lawn Mower That Bogs Down When Blades are Engaged

These steps should help you find the issue with a mower that bogs down when the blades are engaged.

Step 1: Mow More Often

Many times, the problem with a riding mower that bogs down when the blades are engaged is really a problem of too much grass. During the height of the mowing season, grass can grow rapidly, especially if watered and fed properly.

It may be time to raise the level of your mower deck to the next higher setting. In many ways, this is healthier for your grass in the long run. Trying to keep your turf mown too short can stress the plants and cause them to be more susceptible to disease and insects.

If you must keep your lawn mown short, you may need to raise the deck on your mower and make multiple passes over the lawn. You can lower the mower deck each pass until you get the grass to the height you desire.

Step 2: Keep the Blades Sharp

Dull blades don’t cut well and can lead to your mower bogging down in thick grass. Also, dull mower blades damage your turn and can lead to diseases or insect problems. You can look at your turf to get some idea of how well your mower blades are cutting.

Sharp mower blades will leave a clean edge on the cut leaves of grass. The cut edges will not show any tears or browning of the edge. Dull mower blades tear and break the leaves rather than cutting. The damage is easy to spot.

Professional landscapers recommend that you sharpen your mower blades every 20 to 25 hours of use. Homeowners who mow once a week and take two hours to mow should sharpen blades every 12 weeks.

Step 3: Check the Bearings or Bushings on the Spindles

Your mower deck has spindles that support the pulleys on which the drive belt runs. Each of these spindles and pulleys has bearing or bushings that allow the spindles to turn freely. Dirt and debris can work their way into these bearings and cause them to wear and eventually fail.

Check all the bearings and bushings on the spindles for wear. These bushing and bearing should turn freely with no binding or wobble. The spindles on the mower deck are relatively easy to replace. Install new spindles when you notice excessive wobble or tightness.

Many mowers have grease zerts on the spindles and other bearings or bushings. Consult the owner’s manual that came with your mower about how to lubricate these parts. Establishing a proper maintenance routine for your lawnmower will extend its life and keep repairs to a minimum.

Step 4: Belting it Out

A properly adjusted drive belt (or belts as the case may be) can help keep your mower from bogging down. Like the other parts on the underside of your riding lawnmower, the drive belts take a lot of abuse. Examine these critical parts often and replace them when they begin to show wear, cracking, or slipping.

Most newer riding lawnmowers have self-adjusting belt tensioners. These self-tensioners ride against the belt and maintain constant pressure to ensure that the belt doesn’t slip. As the belt ages, it may stretch to the point that the tensioner cannot adjust enough. A new belt will solve this problem and get you cutting again.

Slipping belts on the mower deck can point to a broken belt tensioner. A broken tensioner is not a common problem but can happen. If the tensioner is broken, the only solution is to replace the part. Replacing a belt tensioner is well within the capabilities of most homeowners. Check the user’s manual of your lawnmower for the correct part number.

Step 5: The Governor is Not Governing

Your riding lawn mower engine has an automatic governor on the throttle. When the load on the engine increases, this automatic governor opens the throttle. The governor can be a mechanical linkage in the throttle assembly or computer control.

Mechanical governor linkages often become fouled with dirt, accumulated oil, or other debris from mowing. Most governor linkages have several springs that control the governor’s operation. Examine the entire throttle linkage assembly for damage, missing springs, or debris that impedes the operation.

Electronic governors sense the engine’s speed and use a solenoid to operate the throttle. Diagnosing problems with an electronic governor often require special testing equipment. If you suspect that the electronic governor is not operating properly, you should consult a trained technician.

Step 6: Air and Fuel

Several issues with the air and fuel delivery system can cause your mower to bog down when the blades are engaged. Among the most common problems with the air and fuel delivery systems are:

  • Dirty Air Filter – A dirty air filter may stop your engine from running at full speed and cause bogging down. The engine may start and idle fine, but not enough air can get into the engine when the throttle opens. Check the air filter regularly. Many professional landscapers suggest checking and cleaning the air filter at each fuel fill-up.
  • Old Gas – Gasoline doesn’t have an exceptionally long shelf life. Gas left over from last season can be a problem. Many homeowners have problems with bogging or stalling the first time they start their mower in the spring. Always store your lawnmower with an empty gas tank and run the carburetor dry. Removing the gas before storing it will eliminate many more fuel system problems.
  • Fouled Carburetor – If you did store your lawnmower without running the carburetor out of gas, you might have clogged jets and small orifices. Using one of the many carburetor cleaning products on the market may solve your problem. If the fouling is too severe, the carburetor may need to be cleaned or replaced.
  • Clogged Fuel Filter – A partially clogged fuel filter can prevent the engine from getting enough gas to operate. Sometimes enough gas will pass through a dirty gas filter to start the engine but not enough to run at full throttle. These gas filters are relatively easy and inexpensive to replace.

Step 7: Engine Not Firing on All Cylinders

Many riding lawnmowers and garden tractors have two-cylinder engines. On some models, there have been problems with the engine running with only one cylinder firing. It isn’t easy to hear any difference in the engine sounds when this happens. However, with only one cylinder firing, the mower has only half the power.

Diagnosing this problem is as easy as checking the spark on each cylinder. Start the lawnmower and remove the sparkplug wire from the first cylinder and check to ensure that the sparkplug is working. Repeat the process on the second cylinder.

Other issues can affect the power output of your lawnmower’s engine. A leaky head gasket can significantly reduce the power your engine produces. Bad rings on the piston or a damaged cylinder head can have the same effect. Diagnosing these problems is best done by a trained technician.

Step 8: When All Else Fails

If no other solution presents itself, it may be time to seek professional help. Today’s lawnmowers depend on sophisticated sensors and computer controls to run efficiently. These electronic parts are subject to failure, just like any mechanical part. Unfortunately, diagnosing these sorts of problems is beyond the capability of most homeowners.

If you suspect that your lawnmower’s electronic components are the problem, a factory-trained technician is your best option. Factory-trained technicians and a well-equipped shop have the tools and testing gear to find the problem faster and cheaper.

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A Little Bit of Prevention

Doing a bit of prevention can eliminate a lot of frustration. The manufacturer of your lawnmower includes in the owner’s manual a preventative maintenance schedule. Keeping to this schedule will help lower the chances your mower will suffer unexpected problems. Using the maintenance schedule works to keep your frustration level down and saves you money in the long run.

We hope that this article helps you diagnose and fix your lawnmower when it begins to bog down. Maintaining a riding lawnmower can be a bit overwhelming. A few good tips and tricks can often get your mower operating again. Good luck with your lawn.

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Dennis Howard
Dennis Howard

Dennis is a retired firefighter with an extensive background in construction, home improvement, and remodeling. He worked in the trades part-time while serving as an active firefighter. On his retirement, he started a remodeling and home repair business, which he ran for several years.

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