[b]Affordable Holley four-barrel performance rebuild kits from Quick Fuel Technology[/b]

[b]Story and photos by Joe Woods[/b]


The Holley 600cfm vacuum secondary four-barrel (PN 0-1850) offers a good balance of performance and fuel economy on most small-block powered street rods, and used examples can be found on shop shelves and at swap meets around the country. We thought Holley's little workhorse would be a good candidate for a Quick Fuel upgrade.

Our little four-barrel was a pretty basic carb, tuned more for economy than performance. We decided to upgrade our Holley with a new QFT adjustable billet vacuum secondary module, which allows you to regulate when the secondary throttle plates open, giving the driver added control over fuel economy and power. Originally, our Holley used only one metering block on the primary side while the secondary side made due with a drilled metering plate located inside the bowl. By adding billet metering blocks to both sides, we both improved the fuel flow and provided the ability to change secondary metering to allow for improved performance tuning. By machining the blocks from billet, QFT eliminates the porosity and surface imperfections that cause cross-well bleeding and lost performance in many cast metering blocks.

Most of the parts we needed for this rebuild are included in the QFT Performance non-stick gasket kit (# 3-200). We also ordered a billet primary metering block (# 34-8 ) and secondary metering block conversion kit (# 34-66). The adjustable vacuum secondary kit (# 63-1) rounded out our rebuild parts list.

Source:

Quick Fuel Technology
129 Dishman Lane
Bowling Green, KY 42101
ph 270-793-0900
www.quickfueltechnology.com

Justice Brothers
2734 East Huntington Drive
Duarte, CA 91010 U.S.A.
Telephone: 626.359.9174

What we have here is a staple of American automotive history. It's a basic 600cfm Holley four-barrel, vacuum secondary carburetor with half a decade of accumulated shop crud.

Start with a good carb cleaner, such as Justice Brothers, to remove built up gunk and dirt.

With the exterior and individual bores of the carb clean we are ready to start removing the old parts.

This plastic choke unit is old and brittle, so we will be replacing it with a metal one form another Holley we had in the shop. This is a great opportunity to convert a manual choke to electric. Four screws and a cotter pin hold the choke on. Remove the screws and top half of the choke first.

To remove the vacuum secondary, first remove the c-clip attaching the connecting rod to the secondary throttle shaft.

With the choke, screws and clip removed, pull the old vacuum solenoid away from the main body. There is a small gasket around the vacuum port, be sure to remove the old one and replace it with the gasket supplied with the new solenoid.

The secondary bowl was a little more stubborn, but by prying between the connector tube port and the main body we were able to free it along one edge then lift it away.

The new QFT adjustable vacuum solenoid is held to the main body with the three original screws. This is a good place to start the reassembly, but don't attach the connecting rod until you change the throttle body gasket.

The metering blocks can be a real hassle to remove. We were able to get this one off using a large screwdriver and prying very carefully. If you get to rough with this step you might be buying a new body, so take your time and work it free a little at a time.

An old throttle body gasket can cause vacuum leaks and tuning problems. To replace it, remove the throttle body, which is secured by these six screws.

Each rebuild kit contains gaskets for several sizes of carburetor, make sure to use the right size for the bores on your main body.

Since we are converting this carb to have two metering blocks, the original secondary metering plate will need to come out. These fasteners have a unique head, and while there is a special tool to remove them, we got it done with a small screwdriver.

With the plates off, the gaskets will need to be removed. The new QFT gaskets are coated with florocarbon to prevent sticking, so once installed they make future carb work such simpler and faster.

We chose to install #72 jets in the primary metering block and #80 in the new secondary block. Quick Fuel offers a great jet kit that comes in a locking plastic organizer, ours had four jets each from #70 through #84.

Here are the two blocks together, since only the primary side of this carb is getting a power valve, the secondary block has no power valve port.

Compared side-by-side, the original power valve can't begin to match the flow of QFT's Four Door power valve.

Install the power valve into the primary metering block using the non-stick gasket from the rebuild kit.

Pre-install the gaskets on the metering block before mounting the block to the main body. The gasket will stay in place on the metering block's locating pins.

When rebuilding an older carb, it's a good idea to change the accelerator pump diaphragm, to access it remove these four screws and lift off the cover.

Here you can see the old rotted diaphragm next to the new QFT 30cc diaphragm.

The new diaphragm installs on top of the return spring.

Start each screw by hand then tighten gradually in a cross pattern to avoid distorting the diaphragm.

Guide the gasket and metering block into place on the body before you install the float bowls. Be sure the locating pins are all securely seated in their holes before you try to tighten the bolts.

Hold the float bowls and metering blocks in position and start the four bolts by hand. New bolt seals are provided with the blocks. Be sure to get the accelerator pump arm on the right side of its actuator before you tighten the bowls, if you forget you can always remove the pump cover and reposition the arm.

The old needle and seat is removed by freeing this screw and then turning the nut to unscrew the assembly.

Install the new needle and seat assemblies by simply dropping them into the holes and pressing lightly with your finger to push the o-ring seals into place.

The original connector tube wont be long enough to reach the secondary bowl after we add the new secondary metering block. QFT provides this longer aluminum one with an improved seal design in the correct length.

The connector tube just presses into the bowls using the supplied seals. With the tube in place, we are ready to install the secondary bowl.

Here you can see the difference in lengths between the original bolts and the supplied QFT bolts. Since we are converting this carb from one metering block to two, we need one set of longer bolts for the secondary side.

Install the secondary bowl and metering block with the new gaskets. Be sure the connector tube seats all the way into the bowl as you tighten the new longer bowl screws.

This screw allows adjustment of the vacuum secondary. If adjusted correctly, it will open smoothly without any surge or lag in power delivery.

Here is the finished product, from a useless paperweight to an affordable and totally adjustable performance in a few short hours.


Part Numbers:

Performance kit non-stick gaskets (# 3-200)
Primary metering block (# 34-8 )
Secondary metering block (#34-66)
Adjustable vacuum secondary solenoid (# 63-1)