The jets on the metering block thread in at the front side; the power-valve threads in from the rear of the block. The power valve is rated at a specific vacuum, in inches of mercury. They are usually found only on the primary side but are also installed on the secondary metering block of certain high-performance models.
This is part of the fuel enrichment circuit that opens gradually to full open, depending on engine vacuum. During cruising, the valve is shut. As engine-load demand increases upon acceleration, engine vacuum begins to drop, allowing the power valve to open. Power valves are available in a range of vacuum ratings, which allows you to tailor it according to your needs.
A Holley power valve includes a four-sided head that can be serviced with a 1-inch wrench, but the flats are fairly thin. A dedicated power-valve wrench is highly recommended.
This white plastic piece is commonly referred to as a “whistle.” It aids in preventing fuel from spilling out of the primary vent tube during hard accelerations. They are featured on some carbs but are added easily to those without them.
The primary and secondary fuel bowls and metering blocks have been removed on this typical 4150-series carb. This is a 750-cfm Double Pumper (PN 4779).
Parts that are interchangeable between the 4150 and 4160 series include jets, power valves, floats, needle/seat assemblies, vacuum diaphragm springs (for those equipped with vacuum secondaries), fuel bowl vent components, some accelerator pump hardware, primary bowl gaskets, and, of course, carb-to-manifold gaskets.
Double Pumper
If a 4150 carb has mechanical secondary operation, it has both a primary and secondary accelerator pump, and is referred to as a Double Pumper carb. Depending on the model, 4-barrel carburetors have either vacuum-operated secondaries or mechanical secondaries.
All primary sides include an accelerator pump, which is activated by the throttle linkage. The pump serves to inject an added boost of fuel to eliminate bog or lag when the throttles are opened, which is especially critical at lower engine speeds.
With a vacuum secondary design, the secondaries begin to open according to vacuum developed in one of the primary bore venturis, as engine load increases. During quick accelerator operation under load, a slight delay may be encountered while the secondaries begin to open. You can tune the vacuum secondary by changing to a lighter or heavier spring inside the vacuum diaphragm housing.
Double Pumper carburetors are equipped with mechanical secondaries; a second, separate accelerator pump circuit is located on the secondary side. The secondaries receive an immediate shot of initial fuel from the secondary’s accelerator pump as the throttle linkage progresses.
The 650-cfm 4150 (PN 76650BL) is one of Holley’s Double Pumper Ultra series, featuring billet aluminum metering blocks and a billet aluminum baseplate. The Ultra series is available with various color-coded blocks and baseplate in blue, red, and Hard Core Black.
The Ultra Series 4150 carbs are offered in either mechanical- or electric-choke versions. The Ultra HP series eliminates the choke provision.
Double Pumper carbs are best suited to lighter-weight vehicles, those equipped with a manual transmission, and those with high–stall-speed automatic transmissions in the 3,000-rpm range.
Avenger
Introduced In 2009, the HP-series Street Avenger includes cast aluminum bodies with billet metering blocks and baseplates that reduce overall weight by an astounding 5 pounds compared to previous 4150 carbs. This line of carbs is also offered in both diecast and aluminum body construction. The Ultra Avenger series offers some appearance enhancements such as metering blocks and bodies in Hard Core Black, Hard Core Gray, blue, and red. The lineup is quite extensive.
In 2011, Holley released a new aluminum Ultra HP 4150-series carb with 30 new and improved features, including larger 1.6-inch venturis. The Avenger series is offered in ratings from 470 to 870 cfm, in both street and truck/off-road configurations. Although the majority of Avenger carbs have electric choke, six versions within the entire lineup are offered with manual choke. All Avengers have vacuum secondaries.
Street Avenger carbs were designed and calibrated specifically for optimal street performance, with features including a secondary metering block, four vacuum ports (for positive crankcase ventilation, power brake, spark, and vacuum accessories). The Avenger series is not designed for immediate bolt-on use with Chrysler automatic overdrive transmissions. If used with a GM overdrive TH700R4 or TH200R4 transmission, you need Holley’s transmission kickdown cable bracket (PN 20-95) and geometry corrector (PN 20-121). Depending on your throttle bracket, you also need a throttle stud (PN 20-2, 20-38, or 20-40). The Street Avenger includes a Ford automatic transmission kick-down, but not for use with overdrive transmissions.
The Ultra Street Avenger series has aluminum construction and anodized billet aluminum metering blocks and baseplate (available in various colors). The Ultra is lighter (for those concerned with minimizing weight) and comes in several anodized colors. Personally, I love the Ultra series; in addition to the benefit of reduced weight, they look way cool.
In addition to reduced weight and the obvious visual appeal, the anodizing protects the aluminum from long-term corrosion.
The Ultra Series 4150 carbs has convenient glass fuel bowl sights, making it much easier to check fuel bowl level during adjustments without the need to remove a solid brass plug.
In recent years, black has become the go-to color for those who wish to break out of the chrome-and-color mold and create a pro, understated, somewhat monochromatic appearance. Holley’s Hard Core Black finish has become very popular. This is a 750-cfm Ultra Double Pumper (PN 76750HB).
In the Ultra series, the two letters at the end of the part number indicate color (HB is Hard Core Black, RD is red, BL is blue, etc.).
Holley Ultra 4150 street/strip Double Pumper carbs share the same features, including aluminum construction for reduced weight, billet aluminum metering blocks and baseplate, mechanical secondary operation, choice of manual or electric choke, four-corner idle adjustment, clear sight windows on both bowls, are optimized for out-of-the-box street/strip calibration, and are available in 650 to 750 cfm.
All Ultra and Ultra HP carbs have double-pumper operation with an accelerator pump for each