Power Valve Plug
What does a power valve do? The power valve allows the carburetor to function much leaner for part-throttle fuel economy but once the throttle is in a wide-open position, vacuum in the manifold drops to almost zero and the power valve enriches the fuel mixture. When the engine is returned to basic part-throttle operation and vacuum rises, the power valve closes up, leaning out the mixture. The power valve is important because of its effect on everyday, around-town drivability.
The rule of thumb for power valve size selection is to divide your highest part throttle manifold vacuum reading by two and select the closest size smaller. Example: 8" Hg of manifold vacuum would use a 3.5" Hg power valve. Holley power valves include gaskets (thread size: 1/2-28).
WARNING: Motor vehicles contain fuel, oils and fluids, battery posts, terminals and related accessories which contain lead and lead compounds and other chemicals known to the State of California to cause cancer, birth defects and other reproductive harm. These chemicals are found in vehicles, vehicle parts and accessories, both new and as replacements. When being serviced, these vehicles generate used oil, waste fluids, grease, fumes and particulates, all known to the State of California to cause cancer, birth defects, and reproductive harm.
WARNING: Some dust created by power sanding, sawing, grinding, drilling, and other construction activities contains chemicals known to the State of California to cause cancer and birth defects or other reproductive harm. Some examples of these chemicals are: lead from lead-based paints, crystalline silica from bricks and cement and other masonry products, and arsenic and chromium from chemically treated lumber. Your risk from exposure to these chemicals varies, depending on how often you do this type of work. To reduce your exposure, work in a well-ventilated area and with approved safety equipment, such as dust masks that are specially designed to filter out microscopic particles.
WARNING: The wires of these products contain chemicals known to the State of California to cause cancer and birth defects or other reproductive harm. Wash hands after handling.