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Stationary Engines Discussion Forum

Testing a Magneto on a Briggs and Stratton Motor

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Phil Grigonis

11-20-2003 17:52:01




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I was curious if any one knew how to test a magneto on a 11 hp Briggs and Stratton motor. Some would say to take the spark plug out, lay it against the block, and pull the engine over. Then they would say if you see the spark plug fire a spark, then the magneto must be good. But this is not a proper way to test the magneto because when the motor is under compression it requires twice as much voltage to fire the spark plug. Does anyone know the proper way to test a magneto on a small motor?

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EIL

12-06-2003 21:33:07




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 Re: Testing a Magneto on a Briggs and Stratton Mot in reply to Phil Grigonis, 11-20-2003 17:52:01  
Briggs amkes a tester with a 0.116 gap which if the spark jumps this gap and the plug gap, the it's good. Also briggs suggests testing with an ohm meter. You should get between 2500 and 5000 ohms whe holding the test leads to the plug wire and coil body (ground). However I tried this method and the coil tested fine but was not good.



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brianh

11-21-2003 08:27:36




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 Re: Testing a Magneto on a Briggs and Stratton Mot in reply to Phil Grigonis, 11-20-2003 17:52:01  
Briggs and Stratton makes an inexpensive service tool to check magnetos -- its a 1/4" spark gap enclosed in a plastic housing with a spark plug connector on one end and a big alligator clip for ground attachment on the other. It works great on any spark-ignited engine. I've also seen a lot of homemade test gaps made out of a 1/2" thick slice of 1-2" PVC pipe with machine screws sharpened to a point for the electrodes that work great as well.

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Kent of SW MO

11-21-2003 07:47:39




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 Re: Testing a Magneto on a Briggs and Stratton Mot in reply to Phil Grigonis, 11-20-2003 17:52:01  
I have found that most of the time if a briggs mag will fire the plug in the open with a good blue fire the engine will run. The one B&S engine series this does not work on is the model 9 thru 23 with the Magmatic ignition.



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Baggsy-Wy

11-20-2003 18:23:16




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 Re: Testing a Magneto on a Briggs and Stratton Mot in reply to Phil Grigonis, 11-20-2003 17:52:01  
Double your regular spark plug gap and see if it'll still jump across. Otherwise you have to pull the mag and put it on a tester...



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gary gross

07-30-2005 01:36:58




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 Re: Re: Testing a Magneto on a Briggs and Stratton in reply to Baggsy-Wy, 11-20-2003 18:23:16  
if i have some spark (looks weak to me, but i work on my cars more than my mower) is it still possible for the magneto to be bad on my B&S motor?



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