When you are ready to reassemble the carburetor, all parts must be clean and free of any contaminant and gasket residue. Rather than guessing at fastener tightening, use a calibrated in-lb torque wrench and follow all torque specifications.
Your workspace should be large and clean. Carefully organize all parts prior to assembly. This is time well spent and makes the assembly process proceed more smoothly if you don’t have to waste time searching for parts. Organize the parts in a logical order, starting with the throttle body and main body at the center, with all primary-side parts organized at one end and secondary-side parts at the opposite end. Carefully place all new gaskets and clips next to the associated parts, and so on.
On a clean workspace, begin assembly with the clean main body and throttle body.
This Tech Tip is From the Full Book, HOLLEY CARBURETORS: HOW TO REBUILD. For a comprehensive guide on this entire subject you can visit this link:
LEARN MORE ABOUT THIS BOOK HERE
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To prevent small parts from accidentally rolling off your workbench, consider placing a clean towel on the bench first. Because a towel isn’t smooth like a wood or metal workbench, the small parts are less likely to roll or slide away.
Main Body to Throttle Body Baseplate
Position the main body upside down on a clean workbench; be careful not to damage the vent tubes or choke plate housing. It’s a good idea to place a clean, soft rag or towel on the workbench to avoid damaging the top surface of the main body. Install a new throttle body gasket to the throttle body; align the two small locating dowel pins on the top of the throttle body with the matching holes in the gasket.
Mate the throttle body to the main body carefully; align the throttle body’s dowel pins to register to the bottom of the main body.
Install and tighten all six 12-24 x 3/4–inch screws and torque 30 to 50 in-lbs in a crisscross pattern to evenly distribute the clamping force.
Main Body Assembly
Step 1: Install Main Body Gasket
Position a new throttle body-to-main body gasket. The gasket registers on two small dowel pins. Do not apply any adhesive; install the gasket dry.
Step 2: Torque Main Body Screws (Torque Fasteners)
Tighten fasteners with a 1/4-inch-drive in-lb torque wrench. Any style of calibrated torque wrench is acceptable. This is a digital model from Mac Tools. You simply scroll to the desired torque value, which is displayed on the screen, and press a button. To avoid warping the throttle body, tighten each throttle body-to-main body screw in a crisscross pattern to distribute the clamping load. Final torque is 30 to 50 in-lbs. This digital torque wrench has green LED lights that illuminate progressively as you approach the desired torque; at the selected torque, the lights change to red and the wrench provides an audible beep.
Step 3: Torque Main Body Screws (CONTINUED)
All of the throttle body-to-main body screws should be below-flush with the bottom of the throttle body base.
Step 4: Mount Carburetor to Work Stand
With the main body secured to the throttle body, mount the assembly to a carburetor stand to make assembly easier.
Metering Block Assembly
Using parts from a model appropriate Holley renew kit, install new cork rubber gaskets into the metering block’s idle-mixture-screw hole cavities. To avoid tearing the gaskets, do not use a sharp instrument to push the gaskets into place. Carefully thread the idle-mixture screws into place and gently tighten them until they bottom out, then back off the screws by about 11 ⁄2 turns. Install the power valve and a new gasket into the metering block. Two power-valve designs and related power-valve gaskets are available. It’s important to use the correct gasket; using the incorrect gasket results in a fuel leakage around the power valve. Power valves that have multiple drilled fuel holes must use gasket PN 8R-669. The outer diameter of this gasket is round and it also has a series of three small tangs on the inside.
Power valves with two rectangular window openings must use gasket PN 8R-1597. Both the inside and outside of this gasket are round and it has no inside tangs. Use a 1-inch box wrench or a dedicated power-valve wrench to install the power valve to the metering block. A specialty billet-aluminum power-valve wrench provides enough engagement of the four-flat-side power-valve head to drive the head without coming in contact with the surface of the metering block. This eliminates accidental scuffing or gouging of the metering block. Using a 1-inch box wrench is certainly acceptable, but you must be careful not to dig the wrench into the metering block.
Step 1: Install Power Valve
Thread the power valve into the metering block from the rear of the metering block. Make sure that you install the correct style of power-valve gasket based on the design of your power valve.
Step 2: Install Power Valve CONTINUED (Special Tool)
With the power valve finger-tight, snug the power valve with a 1-inch wrench or a specialty power-valve wrench (shown). This tool properly engages the shallow flats of the power valve, but it does not engage too deeply and therefore prevents marring the metering block surface. After you install the power valve, use a torque wrench to tighten to 40 to 50 in-lbs. Again, be careful not to dig the socket wrench into the metering block.
Step 3: Install Main Jets
Install the main jets in the metering block; use a dedicated jet driver instead of a conventional screwdriver. A Holley jet driver safely captures the jet and eliminates accidental slippage or burring of the jet’s drive slot. The tightening specification for main jets is 30 to 40 in-lbs. Because you can’t use a torque wrench along with the jet driver; bear this torque value in mind. Tighten it snugly but don’t get carried away.
Step 4: Install Vent Whistle
If your metering block was equipped with a vent whistle, install it now. It slips into the top cavity in the metering block with the whistle vent facing the fuel bowl side. Insert a new tap-in rivet pin through the top of the metering block. Tap the rivet pin with a plastic hammer or the grip butt of a screwdriver until the pinhead is flush against the metering block. The pin simply locates the vent whistle and prevents it from dislodging. Set the assembled metering block aside until you’re ready to install the fuel bowl.
Tap the rivet pin with a plastic hammer or the grib butt of the screwdriver until the pinhead is flush against the metering block.
The pin simply locates the vent whistle and prevents it from dislodging. Set the assembled metering block aside until you’re ready to install the fuel bowl.
Accelerator Pump Installation
In this procedure, you are going to install the accelerator pump to the fuel bowl. Only a few parts are required, but these are sensitive parts so this requires a light touch and attention to detail.
Step 1: Organize Accelerator Pump Components
These parts (clockwise from left) are the accelerator pump diaphragm, accelerator pump diaphragm spring, rubber check valve, housing screws, and accelerator pump housing.
Step 2: Install Check Valve (Important!)
Install a new rubber check valve from a renew kit. Handle it with care to avoid tearing. Lightly lubricate the stem of the check valve and pull the stem through the hole in the bottom of the fuel bowl (at the center of the accelerator pump cavity). Pull gently until the stem’s barb has passed into the interior of the bowl.
Step 3: Install Check Valve CONTINUED
Using snips or a razor blade, trim off the excess of the check-valve stem to provide clearance for the float.
Step 4: Install Check Valve CONTINUED
Here, the stem has been trimmed; avoid cutting it excessively. The barb must remain to retain the check valve in place.
Here’s a new check valve installed, viewed from the bottom of the fuel bowl. Make sure that it is fully seated and not distorted.
Step 5: Install Diaphragm Spring (Important!)
With the diaphragm inverted, install the accelerator pump diaphragm spring into the recess (not shown). When installed, the diaphragm must be oriented with the center button facing away from the fuel bowl. This is the contact point for the pump lever. The side of the diaphragm with the shallow rivet head must face toward the recess in the fuel bowl.
Step 6: Install Accelerator Pump Diaphragm
Place the acceleration pump diaphragm in position on the housing, contacting the spring. Carefully align the screw holes of the diaphragm gasket to the threaded holes in the fuel bowl.
Step 7: Install Accelerator Pump Cover
Place the accelerator pump cover and lever assembly in place, start all four 8-32 screws by hand, and then torque all four screws to 5 in-lbs. Be sure that the linkage arm captures the accelerator pump arm.
Step 8: Install Accelerator Pump Cam
An accelerator pump cam, installed on the linkage, controls the opening rate of the accelerator pump. The mounting screw has three positions; three opening rates are possible. The specific carb model’s specifications dictate the factory-recommended position. A single screw secures the cam.
Step 9: Set Clearance of Accelerator Pump Arm and Lever
Initially, adjust the linkage lever at closed throttle to obtain zero clearance between the lever and the accelerator pump arm. Then, move the throttle to wide open. At WOT, check that you have approximately .015 inch of additional travel for the accelerator pump diaphragm arm. To adjust the travel, hold the bottom hex nut while turning the top hex to shorten or lengthen the adjuster’s spring. If you adjust the throttle to a lower idle speed, it moves the pump cam farther away from the lever, which delays the accelerator pump shot. Deal with this adjustment once the carb is mounted to the engine.
Float Installation
Depending on carburetor style, adjustment of the float may be made internally or externally. For a float bowl design that provides no external fuel level adjustment, the float must be adjusted by measuring the distance from the float to a reference surface, usually the bottom of the float bowl. This must be done with the float bowl removed from the carb. For designs with external adjustment, the float level can be adjusted without disassembly. After removing the fuel-bowl sight plug, loosen the locking screw on top of the bowl; this allows the float level to be adjusted. Simply turning the hex nut causes the needle and seat assembly to raise or lower. Some models have a clear sight glass, so removal of the sight plug is unnecessary. Adjustments must be made with the engine running.
Center-Hung Float
The two screw holes on the float bracket align with two threaded holes in the upper area inside the bowl. The pivot pin of the float bracket slides into two side grooves that are below the screw holes. Align the screw holes and use a small flat-blade screwdriver to install the two mounting screws. With a center-hung brass float, an initial adjustment can be made during carb assembly. With fuel in the bowls, adjust the depth of the needle and seat assembly on the engine. With the float, needle, and seat installed, invert the bowl. To adjust the needle and seat assembly, turn the needle’s adjuster nut until the top surface of the float is parallel to the roof of the fuel bowl. Remember that you’re looking at it upside down.
With the float adjusted initially, you should just be able to see the two screws that secure the float’s bracket to the bowl. This provides a gap of about 5/16 inch between the top of the float to the roof of the bowl. This will get you into the ballpark; final float adjustment is made on a running engine. The Holley Renew Kit’s instructions provide recommended clearance dimensions, based on the specific carb model. A primary dry-float adjustment may be 13/16, 3/8, or 11/32 inch. Secondary dry-float adjustment maybe 3/4 to 1/2 inch, again depending on the carb model. The renew kit comes with a handy ruler so you can accurately measure float depth.
While holding the nut secure, use a large flat-blade screwdriver to loosen the locking screw. The object is to adjust the float level to a point at which the fuel level in the bowl just begins to dribble out of the bottom of the sight hole. Rock the engine or vehicle from side to side to slosh fuel back and forth in the bowl. This provides a starting point. Start the engine and adjust the needle until the fuel level is at the bottom of the sight hole, just barely dribbling out. Stop the engine. Hold the adjuster nut stationary and tighten the locking screw.
Fuel Float Installation
Step 1: Inspect Float
When installing a center-hung brass float, make sure that the pivot pin is centered; an equal amount of the pin should be exposed on each side.
Step 2: Install Fuel Float Bracket
Attach the center-hung float bracket via the two threaded holes inside the bowl. The float’s pivot pin seats inside the notches, which are located at the mid-point of the float bracket recess.
Insert the float bracket into the recess with the pivot pin seated in the notches. Secure the bracket with the two 6-32 x 1/2–inch screws and tighten to 5 to 7 in-lbs.
Step 3: Verify Movement of Fuel Float
Check for free vertical movement of the center-hung float; it should move easily. With the fuel bowl inverted, the top surface of the float should be parallel to the roof of the fuel bowl and you should just be able to see the float’s bracket screws. Initially, adjust the depth of the needle and seat assembly to achieve a gap of about 5/16 inch between the float and bowl roof.
Step 4: Install Needle and Seat Assembly
Prior to installing the needle and seat assembly, lightly lubricate the threads and the O-ring with a rubber-safe lube such as Vaseline. This helps to protect the O-ring from damage. Carefully insert the needle and seat assembly into the threaded port on top of the fuel bowl. The upper threads on the brass valve body should engage easily by hand.
Step 5: Thread Adjuster Nut onto Valve
Install a new gasket between the fuel bowl and adjuster nut, and then thread the adjuster nut onto the valve by hand.
Step 6: Install Gasket on Locking Screw
Install a new gasket on the locking screw and thread the locking screw into the brass valve by hand.
Step 7: Adjust Fuel Float
Use a 5/8-inch box wrench on the adjusting nut of an externally adjustable float to hold the nut stationary and prevent it from turning. While holding the adjuster nut in place with the wrench, loosen the locking screw, and then turn the nut to raise or lower the float level. Turning the adjuster nut clockwise lowers the float level and turning the nut counterclockwise raises the float level. Before adjusting, remove the sight plug from the side of the fuel bowl. Place a rag under the fuel bowl to catch any fuel that may spill out of the sight hole. On a running engine, make the final float adjustment by removing the fuel bowl sight plugs.
Side-Hung Float
When installing a side-hung float that offers no external adjustment, carefully bend the mounting tab for final float adjustment. Because of restricted access after installation, float adjustment must be made prior to installing the fuel bowl. With the fuel bowl inverted, adjust until the top of the float is parallel to the roof of the fuel bowl. Refer to the Holley Renew Kit for the specific dimension for your carb part number.
With the bowl inverted, side-hung floats can also be adjusted to a specific distance between the top of the float and the roof of the bowl. The primary float can be adjusted to achieve a 7/64-inch gap between the toe of the float (the portion of the float farthest from the pivot point) and the bowl roof. You can use a 7/64-inch drill bit as the gauge.
This tech tip is from the full book, HOLLEY CARBURETORS: HOW TO REBUILD.
For a comprehensive guide on this entire subject you can visit this link: LEARN MORE ABOUT THIS BOOK HERE
SHARE THIS ARTICLE: Please feel free to share this article on Facebook, in Forums, or with any Clubs you participate in. You can copy and paste this link to share: https://musclecardiy.com/tech-tips/how-to-assemble-a-holley-carburetor-rebuild-guide/