Engine Won’t Start? Ignition Coil Testing, Troubleshooting

Small engine won’t start? This video demonstrates how to test both an ignition coil and a spark plug on a small engine. The ignition coil and spark plug are commonly replaced parts for a small engine that won’t start. Small engines are found in lawn mowers, snowblowers, leaf blowers, edgers, pressure washers, generators, and other outdoor power equipment.

Other commonly replaced parts for a small engine that is not starting are:

Recoil starter
Start switch
Safety switch
On/off switch
Flywheel key
Air filter

Click here to purchase a replacement small engine ignition coil:

Click here to purchase a replacement small engine spark plug:

Click here to purchase the ignition tester used in this part testing video:

How to disassemble a Briggs & Stratton small engine:

For more DIY videos including part replacement and help finding your model visit the repair help section of our website:

All of the information provided in this part testing video is applicable to the following brands:
Briggs & Stratton, Craftsman, Echo, Homelite, Honda, Kawasaki, Kohler, LCT, MTD, Poulan, Ryobi, Tecumseh, Toro

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26 thoughts on “Engine Won’t Start? Ignition Coil Testing, Troubleshooting

  1. One item with " coil failures " is moisture inside the coil itself.
    Begin by cleaning coil contacts ( two magneto contact ear tips).
    A coil WITH MOISTURE INSIDE will ohm out AS BAD.
    after cleaning coil tips; useing an aluminum cake or pie pan, heat your house oven to 250/300 degrees ( pre-heated).
    Place coil in pan and into oven 7-10 minutes.
    Remove coil, anf using CLEAR LAQUER SPRAY, spray coat the cooled down coil all over coil black wound surface including where wire exits coil winding.
    Allow to dry, SAND OFF COIL CONTACT POINTS then re-test with ohmeter.
    If coil tests good, MOISTURE IN COIL " WAS YOUR PROBLEM ".
    USUALLY IF; rust is showing on flywheel AS WELL AS COIL TIPS that air-gaps the flywheel, MOISTURE IS THE CAUSE FOR RUST as well as COIL RESISTENCE FAILURE.
    TOO MUCH RUST between coil and magneto-flywheel REDUCES AIR GAP needed .
    Both flywheel AND COIL TIPS should be cleaned and rust free, AIR GAP RE-SET then spark check conducted.
    Motor should run then.

  2. Hi, My Craftsman model 486.24536 won't start.

    I hop on, depress brake, turn key, engine turns over.

    It has good spark at spark plug (Removed plug, reattached plug wire, turned engine over with end of plug held near metal frame, sparks).

    Checked fuel, also squirted starter fluid in carburetor, turned engine over, won't fire.

    Now wondering about damaged flywheel key. 

    Question: If flywheel key was damaged during use, will tractor quit running immediately?

    The reason I ask is tractor ran fine from the time I finished my job, drove it into the garage, parked it and turned off the key. I come out a couple hours later, hop on, no start….

    Scratching my head, puzzled….)

  3. remember , other models of one piston engines like honda the coils must have a distance ,gap from the flywheel..its better to read the repair manual .

  4. Thanks. I bought that exact same ignition tester and was able to determine that my ignition was good but my spark plug was bad. I installed the replacement spark plug and the mower works fine.

  5. I get no light on my tester when connected to the plug but when I hook it to ground I get a light telling me there is current from the coil. Spark plug is no good right…wrong , I changed the plug and I get no light on my tester same as before. When I disconnect the kill switch my tester lights and when I connect the switch , my tester lights. This Pressure washer Ryobi with a Honda engine) GCV 160 is 7 weeks old and used only 1 1/2 hrs. Now it does not start . It's a POS !!!

  6. I have a FS80R Stihl trimmer,, was running perfect, put it up, when I went to use it the next time has not fired since,, tested the coil by passed the switch as said, switch coils , good plug,, can not get this thing to fire,, any suggestions ?

  7. Changed coils on other vehicles, and no problem. I am A&P aircraft mechanic. So far 3 coils all wiring checked a dozen times. air gap perfect. tested with ground wire off and on. Have tested with spark plug and a tester, and ABSOLUTELY NO SPARK OF ANY KIND!!!! MTD 18 hp. sat outside during very wet winter, and rotor was VERY rusted, but all cleaned up to spotless condition.. NO SPARK! I am lost!

  8. according to a Briggs and Stratton troubleshooting link, these ( more costly) types of testers are specifically designed to also stress the coil for optimacy, especially, having to jump two gaps. There's also the mention of myths about the color of spark, rust on the flywheel etc. But the mention of 250 rpm is to me misleading, except for the peak performance. I've tested the spark or voltage just by hands moving the magnet past the magneto coil back and forth. But I did also notice the points style was far more responsive and the newer coil without points, might require a much higher rpm. http://www.briggsandstratton.com/lam/pt/support/faqs/ignition-system-theory-and-testing

  9. It is not  a genuine spark plug test, it still gives you a reading when the spark is weak  and the engine does not start. If the gap is not ok on a new plug and the spark is weak and the engine does not start  it still tells you the plug is ok, you can waste a lot of time checking for the problem when the problem is actually  the spark plug. There is only one foolproof way,  you have to visibly see the spark. see cde pty ltd tester

  10. I see one problem here he hooks the tester up in front of the mower. Walks to the back holds the break and pulls the cord. How is going to see the tester ? Most of us work alone on this crap. What are we suppose to do use a mirror ? Besides that after I past 50 my eyes are not that great. Even so how is anyone suppose to see that tiny spark so far away ?
    Seems every neighborhood has some brat who's mission in life is to pester the crap out of you. Well I used him and he has not been back. Kind of miss him now. I used the wife but now I got to refer to her as the Plaintiff.

  11. Hello, I have just replaced one engine coil on my mini cooper R56 (2nd generation) 
    The engine and shaking is now fine. I have heard if one goes the other coils will go too. Is that true? Some sources stay they last for a lifetime? What is true? Thanks

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