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Lawn Mower Won't Start? - Top 10 Small Engine Troubleshooting Tips

Updated on December 8, 2017
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Eugene has a keen interest in DIY and gardening. Over a 30 year period he has also become self taught in garden power tool maintenance.

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Lawn Mower Won't Start After Winter

For an engine to startup, it basically requires two things, fuel and a spark. If you aren't getting a spark at the plug or fuel isn't getting through to the engine, known as fuel starvation, the machine will never startup. Bad compression can also lead to difficult starting. After storage during winter, seals, pumps and valves in the carburettor can become gummed up with varnish deposits if you leave fuel in the tank. During the summer, dust, and dirt can block the fuel system or clog filters.

While the information here applies to lawnmower engines, it is equally valid for other small engines used on yard equipment such as portable generators, pumps, cultivators, snow blowers, compactors (wackers), cement mixers etc.

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WARNING!!! Before You Start any Mower Troubleshooting....

  • When working on a mower, remember that gasoline/petrol is flammable. Remove all sources of ignition such as naked flames, stoves, sparks, cigarettes or other hot objects in the vicinity when working on the tank or fuel lines.
  • Disconnect the spark lead if you have to remove any clumps of grass jammed under the deck

  • Keep the carburetor side of the engine upwards to avoid oil spills if the mower is placed on its side
  • Drain the tank if you have to turn the mower on its side If there's only a small amount of gas in the tank, you don't need to do this
  • Check oil level If oil is low, it can cause premature engine wear. If there's no oil left, an engine can quickly seize

Remove the spark lead if you need to clean under the deck or turn the blade. Ideally remove the plug
Remove the spark lead if you need to clean under the deck or turn the blade. Ideally remove the plug | Source
Keep the carburetor side upright. The breather is usually on this side, so this stops oil leaking out
Keep the carburetor side upright. The breather is usually on this side, so this stops oil leaking out | Source

Checking the Oil

Check the oil level is ok before starting. Move the mower to a level surface, remove the dip stick and wipe clean. Replace it and remove again. Check the oil is between the high and low marks before starting. Top up if necessary.

Checking Lawn Mower Oil

Oil level should be between the high and low marks on the dipstick
Oil level should be between the high and low marks on the dipstick | Source

How Do You Start a Small Engine?

  1. Set the throttle to high revs or the choke position. If the engine has a manual choke turn it on
  2. Press the primer button (if fitted) about 8 times
  3. Pull the starter rope quickly, but try not to yank it too hard
  4. Allow the engine to reach top speed before using. If the engine has a manual choke, turn it off after about 5 seconds
  5. Don't use turn on a manual choke again if you need to start a hot engine

A 10 Tip Checklist to Get Your Mower Started

Tip
 
1
Use fresh gas. Don't use old gasoline which can cause difficult starting. Make sure there is enough fuel in the gas tank and check the vent in the tank cap is unblocked
2
Check the spark lead is firmly attached to the plug, and the plug is tightly screwed in. Try replacing spark plug with a new one
3
Make sure the "dead man's handle" control on the mower is held fully against the mower handle while starting.
4
Turn on choke if a manual choke fitted. Don't turn on the choke if the engine has been running in the last 5 minutes or so
5
Make sure primer bulb is pressed about 5 times (if fitted). If the mower runs out of gas during cutting, it will need to be primed again
6
Check the air filter isn't dirty. Wash and dry foam type air filter (see below for details), or replace dirty paper filter
7
Check the cable connecting the "dead man's handle" on the frame to the engine is not damaged or snapped
8
Check the carburettor is tightly screwed or bolted to the engine
9
Make sure there is no water lodged at the bottom of the gas tank
10
If the starter cord is hard to pull, check there are no clumps of grass clippings clogging the underside of the deck. These can jam the blade. Disconnect the spark lead before attempting to move the blade to remove clippings!

More Advanced Troubleshooting.......

If you still can't get your mower started, checkout this guide which covers more in-depth troubleshooting of issues with fuel flow and starvation, the carburetor, ignition system, choke, valves and compression How to Fix a Lawn Mower That Won't Start

© 2015 Eugene Brennan

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    • Larry Rankin profile image

      Larry Rankin 2 years ago from Oklahoma

      Very useful! It's good to have an article like this to reference when my small engines won't start.