Holley 12-883, 12-885, 12-884 Installation Instructions Manual

HOLLEY 2 & 4 PORT BILLET FUEL PRESSURE REGULATORS

P/N

DESCRIPTION

PRESSURE

RANGE

INLET/OUTLET

SIZE

RETURN

SIZE

12-883

2 Port Regulator, Double Adjustable, Return Style

4 to 9 PSI

10AN O-ring in/out

10AN O-ring

12-884

2 Port Regulator, Double Adjustable, Return Style

4 to 9 PSI

8AN O-ring in/out

8AN O-ring

12-885

4 Port Regulator, Double Adjustable, Return Style

4 to 9 PSI

8AN O-ring in/out

8AN O-ring

P/N 12-883, 12-884, & 12-885

Installation Instructions 199R11173

WARNING! These instructions must be read and fully understood before beginning the installation. Failure to follow these

instructions may result in poor performance, vehicle damage, personal injury, or death. If these instructions are
not fully understood, installation should not be attempted.

APPLICATIONS:

INTRODUCTION:

Congratulations on your purchase of the Holley 2 or 4 Port Regulator! Holley Performance Products cannot and will not be responsible
for any alleged or actual engine or other damage, or other conditions resulting from misapplication of the parts described herein.
However, it is our intent to provide the best possible products for our customer; products that perform properly and satisfy your
expectations. Should you have any questions, please call Tech Support at 1-866-464-6553, M-F, 8-6 CST & Sat. 9-3 CST. Please
have the part number on hand of the product when you call.

NOTE: Alcohol engines typically require 3-5 psi at idle and 9-11 at WOT.

Figure 1

INSTALLATION:

1. The double adjustable regulators are designed to work with belt or cable driven fuel pumps where the at-idle pressure and full
throttle fuel pressures require separate settings. In these instructions, we have provided two fuel system diagrams for your
reference. However, we recommend that you follow your fuel pump manufacturers recommendations went plumbing your fuel
system.

2. Connect the outlets of the regulator to the carburetor (if the regulator is installed before the carburetor per Figure 2a). If the
regulator is installed after the carburetor (Figure 2b) the outlet needs to be plugged.

NOTE: The regulator is equipped with the vacuum/boost reference port connection on the cap. This can be connected to full

manifold vacuum to slightly decrease fuel pressure at idle and cruise. This is a requirement on forced induction engines,
so that the differential fuel pressure stays constant under boost.

1

3. The regulator comes from Holley with the regulator pressure preset to approximately 7PSI.

4. However, for individual requirements, it may be readjusted. Loosening the regulator locknut and turning the adjustment screw
clockwise increases the pressure. Decrease pressure by turning the adjustment screw counter-clockwise. Use a fuel pressure
gauge to monitor changes.

WARNING! ALWAYS USE A FUEL PRESSURE GAUGE BETWEEN THE REGULATOR AND THE CARBURETOR(S) WHEN

ADJUSTING THE FUEL PRESSURE REGULATOR.

NOTE: With carburetor set-ups, any change made in fuel pressure will change the fuel bowl float level. A readjustment in fuel

bowl levels will be required for proper and safe operation of the carburetor.

5. Start the engine. With the fuel pressure gauge registering fuel system pressure, check for fuel leaks from and around the
regulator and all fuel lines and connections! If any fuel leaks are found, remove any spilled fuel and repair the leak before
proceeding!

6. If the fuel system holds pressure and there are no fuel leaks, start the engine and hold at
2500-3000 RPM. Set the main pressure adjustment screw of the regulator to the desired operating fuel pressure (regulator is
adjustable from 3-21 psi). Turning the adjustment screw clockwise will increase fuel pressure.

7. Once the desired operating fuel pressure is achieved, tighten the regulator adjustment jam nut.

8. Next with the engine at idle rpm, loosen the jam nut on the idle pressure adjustment set screw (low pressure). Turn counter
clockwise until the desired idle pressure is achieved with the engine running at an idle. This pressure must be lower than the
operating system pressure. Once the desired pressure is achieved, tighten the set screw jam nut.

9. Test drive the vehicle to ensure proper operation and re-check the fuel system for leaks. If any leaks are found, immediately
shut off the engine and repair the leak(s)!

Figure 2a (Carburetor Only)