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Carbon Fouled

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Problem: Carbon fouled
Marked by a soft, sooty carbon deposit. If all of the plugs are carbon-fouled, the plugs may be too low of a heat range; the air/fuel mixture may be too rich; the air filter may be dirty; or you may have a weak ignition, a sticking heat-riser valve, faulty choke or bad fuel injectors. If the problem is limited to a couple of plugs in a set, look for sticking valves, a cracked distributor cap, or bad plug wires.