Lawnmower Repair - Troubleshooting Problems

by James Huntley | Updated 11/01/19

From time to time you might have some trouble with your lawn mower. Many of them are minor and you can save yourself lots of money just by localizing the problem and then see if you can fix it yourself.

The first sign of a problem is often a strange sound, heavy vibration or lack of control. you can sometimes connect the problem with an event like running over a stone on the lawn or the mower refuses to start after you did some work on it.

Before we go any further on this, we have to realize that some lawn mower repairs are specialized and require both special tools and a skilled person to make the work done right. It is not possible for me to cover all brands and types of mowers and you have to realize that any work you make on your mower is on your own risk.

In this article I will start with the most common problems that most owners should be able to deal with.

Lawn Mower Does Not Start

    • Air filter is dirty – Clean or replace the air filter
    • Out of fuel – Fill the fuel tank with fresh gasoline
    • Stale fuel – Empty fuel tank and refill it with fresh, clean gasoline. The old fuel from the lawn mower can safely be used on the car, where it mixes up with lot of fresh fuel.
    • Water in fuel – Empty fuel tank and refill it with fresh, clean gasoline. The old fuel from the lawn mower should be disposed as polluted.
    • Spark plug wire is disconnected – Connect wire to plug.
    • Spark plug is wet or black – Replace spark plug.
    • Loose blade or broken blade adapter – Tighten blade bolt or replace blade adapter.
    • Control bar on handle in released position – Depress control bar to handle.
    • Control bar defective or not working – Replace control bar or cable.
    • Fuel valve lever in OFF position – Turn fuel valve to the ON position.
    • Weak battery (if equipped) – Charge the battery.
    • Disconnected battery connector (if equipped) – Connect battery cable.

Engine is Smoking Thick Gray Smoke

  • Engine oil in the exhaust muffler – Can happen when the mower has been tilted on the exhaust side for cleaning or blade replacement. This isn’t serious and will evaporate and burn in couple of hours.

Light or Medium Smoke, Followed by Uneven Engine Run

  • Gas mixed with oil – Never use  mixed gas intended for string trimmers or hedge trimmers. Replace with fresh gas.
  • Engine worn out and eventually burning engine oil – Engine has to be rebuilt or replaced by a new engine.

Loss of Engine Power

  • Air filter is dirty – Cleanor replace the air filter.
  • Cutting too much grass – Raise  cutting height.
  • Rear of lawn mower housing or cutting blade dragging in heavy grass – Raise cutting height.
  • Buildup of grass, leaves and trash under the mower– Clean underside of mower deck.
  • Too much oil in the engine – Check oil level.
  • Walking speed too fast – Cut at slower walking speed.

Poor or Uneven Cut

Excessive Vibration

Starter Rope Hard to Pull

  • Engine flywheel brake is on when control bar is released – Depress control bar to handle before pulling the starter rope.
  • Bent engine crankshaft – Contact a qualified service center.
  • Broken blade adapter – Replace blade adapter.
  • Blade dragging in grass – Move the lawn mower to cut grass or a hard surface before starting.

Grass Catcher Not Filling (If Equipped)

  • Cutting height too low – Raise cutting height.
  • Lift on blade worn off, wrong blade in use – Replace blade.
  • Catcher is not venting air – Clean grass catcher.

Hard to Push (Push Mower)

  • Grass is too high or wheel height is too low – Raise cutting height.
  • Rear of lawn mower housing or cutting blade dragging in heavy grass – Raise rear of the lawn mower one setting higher.
  • Grass catcher too full – Empty grass catcher.
  • Handle height position not right for you – Adjust handle height to suit.
  • Blade is not sharpSharpen the blade with a file or grinder or replace blade

Loss of Drive or Slowing of Drive Speed (Self Propelled Mower)

  • Drive belt worn out – Check or replace drive belt.
  • Drive belt off the pulley – Reinstall the drive belt.
  • Drive cable worn or broken – Replace drive cable.
  • Loose drive control system – Adjust drive control.

These are things you should check out first if you have a problem. I will go deeper into some of the problems in separate articles.


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