Carl, Non-resistor plugs draw more current which can upset and damage sensitive electronic ignition systems among other things The quote source information can be applied to many of the newer small engines using the same ignition systems.
Resistor vs. Non-Resistor -- Ignition Backlash
On many off-road vehicles, the secondary systems, including resistor spark plugs, are used to reduce the high electrical backlash caused by the coil's primary winding. The backlash, or extra electrical feedback, causes a disruption in the ignition system, such as the CDI boxes and igniters that are part of the ignition control modules. ATV vehicles that do not have such secondary resistor systems can show poor performance, such as periodic missing, rough idle and high-speed ignition cutout. ATV's and motocross bikes use resistor spark plugs to protect the ignition control modules.
Resistor vs. Non-Resistor -- Backlash and RFI
Radio frequency interference can cause disruptive signals to an ATV's sophisticated on-board computer, which links to the control modules. Secondary electrical systems close to the coil will cause backlash and high RFI, since their voltage signal is significantly stronger. Resistor spark plugs suppress RFI and electronic backlash, keeping communication systems clear and on-board computers from harm. Non-resistor spark plugs can cause radio, CB and GPS static interference, as well as disrupt the entire ignition system. Newer ATV models with computer management systems will sometimes not start or run poorly when fitted with non-resistor spark plugs, due to the sensitivity of the computer and module settings.
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