John Deere tractor: no spark when hot

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Old 05-15-16, 10:24 AM
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John Deere tractor: no spark when hot

Hi,I have a john deere[116] lawn tractor w/a 16hp b&s engine.Before mowing season,It wouldn't start and I replaced the magnetron ignition coil with one I bought on ebay and I installed it upside down.Then I went out and bought a genuine B&S.I got a instruction sheet w/that one and realized my error w/the cheap one.anyway I put b&s coil in and away it went.After mowing about an hour,it quit.I couldn't believe I had no spark.I took covers off after it had cooled,it started and ran fine.I wanted to try the ebay coil,so I put that in and ran fine.went out to mow and and it quit after about an hour.I don't know if these new coils have a lower threshold for heat.the 2 coils look identical.All my airways and fins are clean.any ideas?
 
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Old 05-15-16, 10:43 AM
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You checked for spark with a plug grounded and no spark or you made that assumption? A hot coil can fail and work when it's cold. It also shows different resistance values.

It may be the ignition. You have to get a good check for spark right when it quits. It could also be the spark plug heating up and going to a different range or setting on the carb may cool things down.
 
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Old 05-15-16, 10:50 AM
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Are the fins on the flywheel intact? Are you running it with the engine shroud in place? What engine do you have?
 
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Old 05-15-16, 11:49 AM
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no spark when hot

Thanks for replies.the engine is a 16hp b&s twin cyl 402707 0148.I used an inline spark tester and I also grabbed the plug wire and am positive there was no spark.all flywheel fins are intact and clean.all shrouds and covers in place.
 
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Old 05-15-16, 07:37 PM
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With the inline tester it could still have a bad plug, but since you had the courage to hold the plug wire that says a little more. Did you put a screwdriver into the plug wire to make the connection? If so you could say definitely no spark. You did this on both wires - same result?

All you have to do to isolate it to the coil is disconnect the little wire going from the kill to the coil. Then run it until it quits and check for spark. No spark - bad ignition module.
 
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Old 05-15-16, 09:35 PM
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Those engines are notorious for this problem. I don't know why that coil is so prone to that problem, but it is. I was hoping you had a single cylinder and I would have said to check the kill wire, it might be pinched behind the starter. Not on this engine though.
 
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Old 05-16-16, 12:55 PM
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no spark when hot

Hello,and thanks for replies.I've ordered another coil w/an older part#.the picture on ebay shows not like the 2 I got that fail on heat.loc
 
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