Holley 12-840 Carb Fuel Pressure Regulator — 4.5–9 PSI

Dial in steady carbureted fuel pressure with a compact, billet regulator. Adjustable 4.5–9 PSI, non-return (dead-head) design, with one inlet and dual outlets for easy split feeds. Includes a 1/8" NPT gauge port and mounting bracket.

Why builders choose this regulator

Carb-perfect range: adjustable 4.5–9 PSI for street/strip carb setups.
Simple plumbing: no return line needed; one 3/8" NPT inlet feeds two 3/8" NPT outlets.
Easy monitoring: built-in 1/8" NPT gauge port for at-a-glance pressure checks.
Reliable build: billet aluminum body—black base with clear top—for corrosion resistance.
Flexible input: works with electric or mechanical fuel pumps.

Specs

Parameter	Detail
Adjustment Range	4.5–9 PSI (ships preset ~7 PSI; adjust as needed)
Style	Non-return (dead-head)
Ports	Inlet: (1) 3/8" NPT female • Outlets: (2) 3/8" NPT female • Gauge: 1/8" NPT
Vac/Boost Reference	None
Finish	Black anodized base / clear anodized top (billet aluminum)
Mounting	Bracket included
Fuel Compatibility	Gasoline; compatible with ethanol blends (see system guidelines)
Best For	Carbureted street/strip, dual-outlet feeds, mechanical/electric pumps

Great for

Stabilizing pressure to Holley-type 4150/4160 and other performance carbs.
Dual-feed bowls (use the twin 3/8" NPT outlets to split left/right).
Street/strip builds that don’t want to run a return line.

Install notes

Plumb pump → regulator inlet → outlets to carb(s). Cap any unused outlet.
NPT threads: use fuel-safe PTFE paste on NPT threads; do not use sealant on AN flare seats.
Set base pressure with the engine idling and pump running; verify under load.
Carb only: not for EFI systems—use an EFI regulator with a return line.