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[Guido]

DON'T change the plugs because of that "test". Like mentioned above, that will only tell you if the ignition is working, not how accurate. At 1000 RPM you will have almost 10 sparks per second - can your brother's friend count that fast to make sure each spark is happening at the exact time? I doubt it.

If the engine runs fine you probably don't need plugs. Follow the maintenance schedule and let that guy play around with his own engine - not yours.