Lawn Mower Won’t Start: Fuel, Ignition and Compression Problems

This video from Sears PartsDirect shows what to do if your walk behind lawn mower won’t start. There are a number of issues that could be causing the problem. A clogged air filter can keep air from getting to the carburetor and mixing with the gas. You could have a bad spark plug, or you could have an issue with old or contaminated fuel. We’ll show you how to check engine compression, check your fuel tank, clean your fuel line and how to access and examine your choke linkage, return spring and carburetor. This video will take you through the troubleshooting process step-by-step so that you can figure out what’s wrong and learn how to fix it.

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The video includes these parts. Look up your model to make sure you get the right parts for your lawn mower.
Air filter
Spark plug
Gas tank
Ignition Coil
Choke linkage
Carburetor rebuild kit

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38 thoughts on “Lawn Mower Won’t Start: Fuel, Ignition and Compression Problems

  1. I'm a DIY'er for life. I fix my cars and motorcycles and everything else I have encountered in life to date, at 62 yrs young I have met my first lawn mower. I went surfing for help with the troubleshooting for this mower that won't remain running after I put some gas into the compression chamber as a troubleshooting step beyond verifying that there was spark to the new plug.
    I came across your video. I just wanted to say thank you. this is a great job of adding video for each trouble shooting problem. great job. Thanks again.

  2. Is it possible to be the gas cap. The yellow gasket broke off. It starts but stalls out. I sprayed starter fluid and it ran but then stalled again.

  3. totally wrong about the comment about if the screen in the tank is bad you need a new fuel tank wrong add a fuel filter 3 dollars instead of 50 dollars for a tank

  4. Thanks so much appreciate your help. I only used it once so it has to be starter fluid because everything looks clean if not that stabilizer again Thanks for sharing Deb

  5. You should never us starter fluid or ether to try and start the engine, using this fluid can blow your engine apart and you will get hurt bad if it does. Instead use a little   gas in a spray bottle and squirt some into the carb and try and start the engine that way.

  6. I like how MARSOC's official YouTube channel favorited a video on how to diagnose problems in a Lawn Mower. Guess even the most Elite of Marines are still prey to the notorious Green Weenie

  7. you wont always get compression on the tester, i fixed mowers with no compression reading but after I fix the problem such as timing, it works, so a tester is not always correct.

  8. Please explain the phenomena of double grounded spark plugs. Outside of cylinder I have spark. Inside has no spark. I'm still studying this issue, thanks

  9. use premium fuel in small engine , for some reason it works better and does not gum up in a carburetor after long storage ,
    second if you have a fuel valve turn it off while the engine is running and wait until the fuel dries out from the carburetor ,
    Fuel left in the carburetor for a long time will dry up and damage the carburetor , installing a fuel shut off valve is easy ,
    If engine is hard to start remove the spark plug and use a propane torch burn off the Corbin residue and whatever might be on the spark plug , I do it until the Central Electric and the ground electroid get red hot , of course wait until the spark plug cool down before reinstalling it , in the Old Country Palestine we used to put a small amount of gasoline on the ground put the spark plug in the middle of it and set it on fire , that always worked to get us out of a jam ,

  10. I have a 917258550 riding lawn mower. This belonged to a previous owner. I am trying to get it going. I can't get a spark from the spark plug. I have placed my thumb on the spark plug hole and turned it over. It pushed my thumb away! So I do have compression. How Much exactly – I do not know yet! I know it should be between 60 to 100 for this mower. I will get a guage eventually and check it.
    No matter this brings me to the spark plug spark. I have replaced the spark plug and ignition coil. I gapped it to .011. I have unhooked the kill/grounding wire from the back of the ignition coil and still no spark!!!!!!!! What would be next to check????????????????? My best guess is to get a new flywheel for the magnets. Does the magnets on the flywheel have anything to do w/ the spark plug spark???

  11. Why do a compression test on a engine that's got a centrifugal decompressor in it?? It will give a total false reading you could never pull it over fast enough to give you a good reading a leakage test is the best way

  12. Good video but he forgot to mention that before you take apart or mess with the Carburetor to check the fuel filter blow screw on the bottom and holds the bottom bowl section in Place. On some models it's the gas jet for the carburetor. Dirt in the bowl clogs the holes in the hollow screw and no gas goes into the Carburetor throttle Plate. Use a small wire or compressed gas to clean out the hole. Use lots of Caution if you use air, as to much air pressure can blow the screw/jet out of your hand..

  13. Craftsman riding 21 hp mower will not roll over with spark plug in (will with plug out). Checked intake and exhaust valve settings. Done to specifications. Still will not roll over. What suggestions? Thanks!

  14. Hi I left gas in my mower over the winter, now it won't start. I replaced new gas, and the mower would only start after I tilt it to the right. Then it would stall within a few seconds. I repeated the process over about 10 tens and it still does the same. Can you please provide some pointers? My mower is craftman, looks the same as yours, could be the same one. It's a 6.75 engine. Thanks in advance for your advice.

  15. this video does not adress the fact that all these three things need to happen at the right TIME. also, "right amount of compression to drive the piston." this is parcially incorrect. though these three things work together to drive the piston, it is not the job of compression. the job of compression is to compress the fuel/air mixture to the point where it is combustible. I'm surprised that sears got this wrong

  16. I have a lawn tractor that wont start. I need help.
    I replaced the spark plug, oil, oil filter, carburator, fuel pump, fuel filter, and the air filter

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