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

  • Lawnmower Not Starting
  • Crimping lawnmower cables
  • Checking coil and points on lawnmowers

Lawnmower Not Starting

Problems with engines not starting usually come down to either an electrical problem and no spark at the plug, or lack of fuel. Initially though, you should ensure that you are following a proper start-up procedure for the mower:

The procedure for starting an engine is as follows:

  1.  Check that you have the throttle in the start position and/or on high revs with choke on
  2. Prime the engine by pushing the primer button (if fitted) about 5 times 
  3. Pull out the cord until you meet resistance. Then let the cord return fully back into the engine and then pull the cord out sharply. Repeat this until the engine starts but not more than a few times 
  4. If the engine doesn't start, try pressing the primer button another few times then try to pull start the engine 
  5. If the engine doesn't start after a few pulls it may have flooded so leave it for a few minutes before pulling the starter rope

If you still don't have any luck getting the mower started, it's time to start fault finding but remember to check the obvious first !

  1. Ensure you are using fresh gas, old gas is less volatile and may cause difficult starting
  2. Check whether there is a vent on the fuel tank cap and that it isn't blocked 
  3. Check the throttle cable is actuating the linkages at the carburetor 
  4. Firstly check the high-tension lead to the spark plug isn't loose. Remove the spark plug and place the body of the plug against the engine so that it is grounded. Check there is a spark when the engine is cranked. If no spark, there may be a short circuit or crack in the white insulation part of the plug (which can open up when the engine gets hot causing it to stop running) so temporarily try another plug to see if you get a spark. Don't actually use this in the engine unless it's the same time type as it may result in engine damage if it's too long. If this still doesn't work, there may be a problem with the cut off switch, which cuts the engine when the safety handle is released, if this is the case it may be necessary to strip the cowl off the top of the engine to trace the wire and switch 
  5. Ensure air filter is clean. Foam elements can be washed with hot water and detergent, squeezed dry in a cloth and re-oiled with a teaspoon of engine oil spread through the foam. Paper elements can be cleaned with compressed air blown from the inside of the filter but ideally should be replaced 
  6. Check fuel lines aren't kinked or blocked restricting fuel flow 
  7. Ensure fuel filter isn't dirty. This is probably located at the end of the fuel line in the tank 
  8. With the air filter removed and choke off, look into the carburetor intake and check the primer button is drawing fuel up into the carburetor when pressed several times
  9. Check the air filter isn't dirty and the choke plate is opening fully when the engine is running. If the carburettor has a float bowl, remove it ( hold a container under it to collect the fuel) The float and bowl work like a toilet cistern keeping the fuel at a constant level in the bowl. Check the fuel shuts off when the float is pushed upwards. If it doesn’t, the valve that cuts the flow may be dirty or there may be particles of dirt in the fuel preventing the needle on the float from shutting the valve allowing the gas in the bowl to overflow into the carburetor. Examine the float, it may be punctured and sinking in the fuel. Clean out any dirt which has accumulated in the bowl.
  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!

Crimping lawnmower cables

Here's a tip on how to crimp the end of a lawnmower throttle or clutch cable if you don't have a crimping tool.
The terminal blocks commonly used for joining electrical cable contain a small metal block with two screws. The plastic of the terminal block can be removed to extract this block. The block can then be slipped onto the end of a cable and the screws tightened. Alternatively the end of the cable can be passed through the connector and a loop formed by passing the end back through the connector. Cables can also be joined together using the connector. In this case the cables should be overlapped so they are caught by both screws.
The advantage of using a terminal block connector is that it can be re-adjusted and moved to any point on the cable.

Checking coil and points on lawnmowers

One of the points should connect to the coil and the other to ground, With the points open and the kill switch for the engine off i.e. open circuit, measure the resistance from ground to the other end of the coil which is connected to the points. If this is infinite, the coil has gone open circuit or is not grounded properly. Normally the resistance should be a couple of ohms falling to near zero as the points close. If the resistance doesn't fall, check the points aren't dirty or corroded. they can be cleaned with fine sandpaper and IPA but dont overdo it as the points are given a coating to resist arcing and this can be worn away if you rub too hard.
Try a new spark in case this is the problem.
Possibly the spark lead isn't making contact with the end of the plug in the spark plug booth.
Check the kill switch for the engine isn't shorting out the coil, it should be open circuit when the engine is running.


  1. I also had some problems regarding my Lawnmower, just found out some important details and tips on how to fix it. Thanks for this I didn't need to go to a technician. I'm also looking for an info regarding Power Sport Spark Plugs. Thanks in advance.

  2. Hi Herbert. Thanks for the comments! There doesn't appear to be any info on Federal-Mogul's page about these plugs. However you could try requesting info on their contact page here