Posted by Zeke Boniface on July 03, 2015 at 04:27:43 from (74.106.193.208):
In Reply to: Coil Polarity posted by Steve@Advance on July 02, 2015 at 19:41:28:
From SM-2093-(Jul-73)[Service Manual for JD 140 lawn tractor]
Wrong polarity of the coil is not a serious problem, but it can cause damage over a long period of time. A coil that is connected incorrectly will require an extra 4000 to 8000 volts to create a spark.
A coil that is wired correctly will have the same polarity as the battery, figure 12.If the battery has a negative ground, the coil negative terminal should be connected to the breaker point lead. If the battery has a positive ground, the coil's positive terminal should be connected to the breaker point lead.
The wrong coil polarity makes the center electrode of the spark plug have the wrong polarity. This can cause misfiring as voltage requirements increase.
One method of checking polarity is to connect the negative lead of a volt meter to the spark plug terminal. With the engine running, momentarily touch positive voltmeter lead to a ground. The coil polarity is correct if the meter reads up scale.
Another method is to hold the spark plug wire terminal about 1/4 inch from the spark plug. Insert the lead point of a wooden pencil between lead [plug wire "lead", I think they mean-Z.B.] and spark plug,figure 13. Spark should flare and turn orange on the plug side of a pencil lead if polarity is correct. [you'll want some insulation between the pencil and your fingers-Z.B.]
A loss of engine power is also evidenced if coil polarity is reversed.
[End quotation]
Comments? I'm guessing the meter test should be done with a robust analog meter...
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