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Briggs 300421 12HP Coil Issues ?


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My Briggs 300421 12HP would not start this spring, but ran last fall. Just sat in shed all winter. I hookup my inline spark tester & no spark when hooked to spark plug. When I hook it or ground directly to the head it shows good spark.

I tried 3 different condensers, no luck. I disconnect the kill switch wire to coil to isolate the coil & still same problem . I even wiggle the kill switch wire while cranking, no luck. I figure I have a bad coil so I pull the engine & covers.

With the engine on the bench I wiggle the coil wires & crank the engine over with a drill. Still same exact problem no spark hooked to spark plug, & spark when ground to engine. The coil grounds to engine are all clean. The coil gap should be set correct, because I had it apart the year before. I had set the gap & repaired a ground wire that had broken back then.

I remove the coil to Ohm it out. Spark plug wire to each of the little wires I get 4470 ohms. Spark plug wire to each leg of coil I get nothing. I even scratched & cleaned each leg of the coil still nothing.

Unless I'm mistaken I believe I have a bad coil. The problem is I have 5 coils laying around & all 5 test this way. 2 are from some other engines, 1 is the origonal, 1 is a new aftermarket ebay one, & 1 is a NOS Briggs I just got off ebay because I don't trust the aftermarket ones now.

Am I losing my mind or do I have all these bad coils or possibly both. This is the way to test a coil correct ? Should I order a used coil off a running engine ? Briggs Part #298968. Anybody have one for sale ?



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Did you try a different/new  plug. If the spark tester shows spark when you ground it without the plug in the circuit it has to be the plug.

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No I didn't try a different plug. The coil is off the engine already. The coil seems to test bad (internal open) when I ohm the plug wire to the coil stack leg. I get infinite reading & it should be between 2500 to 6500 ohms. 

Can anybody confirm this is the way to ohm out the coil ? From what I researched it is. I'll start looking for another coil. Thanks.

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FYI, I have converted all of my running B&S CI engines to magnatron electronic ignitions and I will not go back to points ignition.

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