Low Pressure Regulator

The HOLLEY Low Pressure Regulator (HLY12-804) is a precision fuel system component engineered for street and strip applications where fine control over fuel pressure is critical. Designed for carburetor-fed and low-pressure fuel injection systems, this in-line regulator maintains steady fuel delivery between 1 and 4 psi—the ideal range for naturally aspirated engines and carbureted platforms. Whether you're tuning a vintage hot rod, maintaining consistent jetting on a street machine, or dialing in fuel curve on a weekend warrior, this regulator eliminates pressure fluctuations that cause lean-running conditions and erratic idle quality.

Built from aluminum construction with chrome plating for corrosion resistance, the HOLLEY regulator features 3/8 inch NPT inlets and outlets—a standard port size that integrates seamlessly into aftermarket and OEM fuel lines. The adjustable diaphragm design responds directly to vacuum and pressure changes, maintaining consistent fuel delivery across throttle transitions and load conditions. At just 0.64 lbs and compact dimensions (3.6 x 2.75 x 3.65 inches), this regulator fits tight engine bays without requiring extensive fuel system modifications or complex mounting brackets. The chrome finish resists corrosion in harsh underhood environments while delivering the clean aesthetics expected in show-quality builds.

Mechanics and engine builders trust HOLLEY fuel regulators for carburetor tuning, vintage restorations, and high-performance street applications. This in-line configuration works equally well on gasoline-powered vehicles with mechanical or electric fuel pumps, making it a universal solution for carbureted engines and low-pressure EFI conversions. Installation is straightforward—simply splice the regulator into the fuel line between the pump and carburetor, adjust the pressure to your jetting specification, and monitor idle quality and throttle response. Compatible with any fuel system using 3/8 NPT ports, this HOLLEY regulator pays for itself through improved fuel economy and eliminated hard-starting issues caused by pressure creep.