Upgrading a 4160 Carburetor to a Secondary Metering Block

Words And Photos: Jeff Smith

There are easily as many different Holley four-barrel carburetors as there are social media opinions about the Kardashians. Luckily, Holley carburetors don’t act like divas and serve a useful purpose in terms of the betterment of mankind. If you are new to the Holley carburetor game, you might be confused by the sheer number of different carburetors. This may steer you toward the less expensive street version carburetors like the 600 cfm 0-1850 or the larger 750 cfm 0-3310C. These two are the most popular of all Holley carburetors as vacuum secondary, four-barrel versions that are reasonably affordable. These two are also somewhat universal that will work well on 300ci engines as well as mild 454 big-blocks. While you could take your chances with a used orphan from the swap meet for about $150, you can almost assume you will be buying someone else’s problem. If that cheap, swap meet Holley works so well, why isn’t it bolted on somebody’s engine?

For the sake of this story, we’ll assume you’re new to the Holley carb game. In order to make these carburetors affordable, Holley has removed a few of the features found on their more expensive cousins. Holley classifies both mechanical and vacuum secondary carburetors into two generic families: 4160 and 4150 versions. The 4150 is by far the most popular and most desirable and can be identified by its thick metering blocks used in both the primary and secondary sides of the carburetor. A 4160 version uses a thin, secondary metering plate that is bolted to the main carburetor body hidden from sight by the secondary fuel bowl.

While the 4160 style carburetors function as intended, the secondary metering plate uses fixed orifices to meter the secondary fuel. On the primary side there is a metering block with replaceable jets which makes primary jetting changes easy. With 4160 carbs, changing the secondary jetting requires replacing the metering plate with the appropriate fixed main metering holes either larger or smaller. There’s nothing wrong with tuning the air-fuel ratio this way except that swapping these plates can get expensive when each new plate costs roughly $30. But do not fret as Holley offers a simple secondary conversion kit that makes secondary jet tuning easy.

We will be dealing with the dual inlet 0-3310 style 4160 Holley carburetor in the photos. The 0-1850 is a single inlet carburetor so that specific kit will come with a longer fuel transfer tube that connects the primary float bowl with the secondary as the fuel feed. Of course, you can also convert the 0-1850 to a dual inlet. This will require a new primary and secondary float bowl conversion kit (PN 34-2), which is pricey at nearly the cost of a new carburetor. You could, of course, do the conversion with used bowls.

The secondary metering block sap is easy to accomplish but there are details things you need to know. The most important aspect is that the new metering block will stretch the length of the carburetor by roughly one inch. This may not seem like a big deal – unless you have a fixed-length 4160 dual inlet fuel feed line. With the thicker metering block, the 4160 dual inlet fuel line will be too short. There are several ways to accommodate this – the easiest being a new, longer fuel line that is offered by dozens of companies. We’ve listed a few options in the Parts Guide.

The Holley conversion kit comes with the new metering block, longer fuel bowl screws, and new gaskets but because of its universal nature, it does not come with secondary jets. We have included a chart of the numbers stamped on the front of the metering plate that lists the equivalent jet size so you know what jet is necessary to complete the swap. It’s best to start with the carb’s original secondary jetting and then invest in jet sizes on either side of stock for both the primary and secondary sides. For example, if the 4160’s secondary metering plate is equivalent to a 77 jet, a pair of 75 and 79 jets would be useful. The only real challenging part of this entire conversion is the need for a small clutch-head screwdriver to remove the metering plate screws. You can find inexpensive clutch head screw drivers online or Sears for example. In a pinch you can sometimes remove these screws with a small straight screwdriver.

Upgrading a 4160 Holley to a metering block is a very simple procedure and should only require a few moments. Just remember to add the appropriate size jets to the metering block. With this simple modification, you now have a full-service Holley carb that is ready for quick jet changes on your way to carburetor tuning stardom.

Metering Plate to Main Jet Conversion Table

Parts Guide

Sources

Holley Performance Products
holley.com