Bought an older rig last year and want to change the spark plugs/wires. I downloaded the onwers manuals and it recommends NGK PZFR5F-11 (1998 Heavy Duty), NGK ZFR5F-11 (1998 Light Duty), and Champion RC10-ECC (1997). Which should I use? What does it mean by Heavy Duty/Light Duty?
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