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Just buy some plugs, install 'em and run 'em for a while. To check the heat range, pull a plug and look at the ground strap. There will be a color change or a point somewhere on the strap where it changes appearance as a result of the combustion process. You want the change to occur at about the point of the bend in the strap. If it changes closer to the tip of the strap, then the plug is too cold. If it changes closer to where the strap is welded to the spark plug body, then the plug is too hot.
For checkin' lean/rich fuel mixture, hold the plug with the ground strap toward you, like you're lookin' down into the ceramic insulation. On the very end of the spark plug body, at the end of the threads where the strap is welded on, there will be deposits of the combustion process. What you want to see there is a light gray color, like a cigarette or cigar ash. Lighter will be too lean, darker will be too rich. Oily will indicate a problem, such as an internal vacuum leak from the crankcase. If the bottom of the intake manifold ports are not sealed to the head on the crankcase side, then the oily vapors from the crankcase will be drawn past the leak and into the combustion chamber when the motor is on the intake stroke.
Last edited by techinspector1; 10-01-2011 at 11:25 AM.
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