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Enlarging Idle Feed Holes

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Truck engines with larger-than-stock cams generally give the carb less vacuum signal and therefore don't draw as much air and fuel through the carb at idle and low-throttle opening. If the mixture screws are threaded out too far and the engine still won't idle correctly, this is probably the case with your engine. To cure this, Murphy first enlarged the idle feed holes in the baseplate that provide air at idle.