Lawn Mower Won't Start? 10 Top Troubleshooting Tips for Small Engines

Updated on April 30, 2018
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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.

Snow blowers use 4 stroke engines just like lawn mowers
Snow blowers use 4 stroke engines just like lawn mowers | Source

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 turn a manual choke back on 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 my other 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

Questions & Answers

  • I replaced the magnetic pick up my mower, but there is still no spark. What can I check next?

    Replace the spark plug, check the ground on the primary is making contact with the engine block and check spark lead and make sure the kill switch isn't shorting out the primary when the throttle is set to the run position.

  • If I put starting fluid in the carburetor and it still does not start, can you pass over the carburetor in troubleshooting as a none starting problem?

    You don't have to troubleshoot in sequence. If you want you can check the spark plug, connections, air filter, etc. first. The important thing is to check or change one thing at a time and see the results.

  • How do I check for a spark on a lawn mower engine ?

    Follow the procedure mentioned in my article:

    1. Find a shaded location.

    2. Remove the plug.

    3. Attach the lead back onto the plug.

    4. Hold the plug threads against the engine block.

    5. Don't touch the lead or the plug!!

    6. Pull the starter cord.

© 2015 Eugene Brennan

Comments

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    • profile image

      JON 

      2 months ago

      THANK YOU !

    • Larry Rankin profile image

      Larry Rankin 

      3 years ago from Oklahoma

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

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