Adjusting the Carb Jetting
Whether you have a Demon™ or a stock HOLLEY® carburetor (or a flow-modified BG model), jetting should be fairly close if the carburetor is used in the intended application. For maximum performance, increase or decrease jet size two numbers (primary and secondary) as required. As long as the performance continues to improve, continue increasing or decreasing jet size. At some point, ET or lap times will start to fall off, which means the mixture has been moved past the optimum air/fuel ratio. At that point, move one jet size at a time in the opposite direction until optimum performance is achieved.
Always jet for performance, not spark plug color. Most high-energy ignitions will leave very little residue on the plugs. With a drag car, plugs can remain bone white so attempting to “read” spark plugs is a waste of time. With an oval track car, the plugs will color, but the process takes longer with a high-energy ignition. If the car runs a little too hot, jetting up one or two sizes will alleviate the lean condition without hurting performance, because the ignition will burn off the extra fuel and cool the engine. However, if jet size is increased but the engine appears to be running leaner, a fuel system problem is indicated. If a conventional ignition is used, jetting for best performance is still the way to go, but the plugs will take on a tan color after a short time.


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