I expect in both cases it was just that the old plugs were worn. Any suitable plugs that are new and have a correct gap, will cause the engine to run a lot sweeter than a old worn set.
The gaps get bigger and bigger as the electrode wears down. Eventually you reach the point that the gap is so big, you no longer get a spark.
The gaps get bigger and bigger as the electrode wears down. Eventually you reach the point that the gap is so big, you no longer get a spark.
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