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I have a Craftsman Trimmer and I'm was not getting a spark when starting it. I tested it with a spark tester and had no spark. I next removed the ground wire from the magneto to isolate it from the starter circuit, but still had no spark. I removed the magneto completely and was about to replace it, but decided to put it back on after a few days and re-test it by turning the flywheel with a cordless drill. I thought I may not have been turning the flywheel fast enough, well I got spark both with the spark tester and with the spark plug. I then replaced the ground wire on the magneto, but I got no spark. Then I decided to test the magneto again with out the ground wire and lo and behold, I got no spark. Reset the gap, but I'm back to no spark. Could there be something that killed the magneto after I put the ground wire back on?

  • I think there is a flaky electrical connection somewhere which you are affecting each time you take parts of or put them back. – wallyk Sep 18 '15 at 3:28
  • Did you get a new spark plug? Or did I misunderstand? Was the only time you got a spark was using the drill? I had to learn how to maintain, fix these 2 stroke machines and learn fast. I took my stuff to a great small engine place and HUNG OUT. They taught a great class (of just me) for free...well, we established a long term relationship, I was able to do simple maintenance and a bit more, put the right gas, mix the right amount of oil, replace filters and keep the dirt out of my machines. When I HAD to get machines fixed, they put me ahead of others. – stormy Sep 22 '15 at 0:06
  • Besides keeping these things clean...keeping dirt out of the works...use non-ethanol gas...one other item for a trimmer (string trimmer for grass edges and light weeds?)...make sure the line doesn't get too long. If you are using the bump 'n go heads check that the cutter is cutting the line. I always take this type of head off and replace it with a straight head where I just cut off a line, thread it, adjust the length by cutting and melting the line on concrete or large rock. You'll hear the engine tune as the line gets to the proper length and balance. Wear glasses and watch upline! – stormy Sep 22 '15 at 0:12
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You can test your magneto (can also be called a coil) directly to see if it works. If you have the coil off of the engine, you can do a resistance test on it to see if it's fried. I don't know what the exact make of the engine is, since Craftsman power tools utilize many different brands and re-brands them. It could be a Briggs and Stratton, but more than likely it's something else. Here are the testing steps for a B&S, but it should allow you to test yours and get an idea if the coil is at issue:

NOTE: Here is a video of how to test it.

  1. Remove the magneto
  2. Get your ohm meter and set it to 20k ohm setting
  3. Place the positive (red) lead to the metal part inside the spark plug wire lead
  4. Place the negative (black) lead to a ground spot on the magneto body (is usually the laminated metal part which bolts to the engine)
  5. Take the ohm reading

The reading should be between 2.5k to 5k ohms (for a B&S, anyway). If less than that or you have direct connectivity, you most likely have a ground fault where it will not produce a spark (the energy created goes directly to ground). If you have greater resistance than that (higher than 5k ohms or even infinity), there is too much resistance. Either way, you'd need to replace the magneto.

If it is looking good, you may also want to try and move the spark plug lead around while you are testing to see if the reading changes.

From your description it appears your magneto is having a ground fault issue. Until you measure it you won't know for sure, though.

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