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.
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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.
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
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)
Step 4: Mount Carburetor to Work Stand
Metering Block Assembly
Using parts from a modelappropriate 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
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.
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
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
Step 4: Install Check Valve CONTINUED
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
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.
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.
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 may be 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
Step 2: Install Fuel Float Bracket
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
Step 6: Install Gasket on Locking Screw
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.
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, sidehung 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.
Metering Block Installation
The secondary float may be adjusted for a 13/64-inch gap between the heel of the float (the area of the float closest to the pivot point) and the roof of the bowl. You can use a 13/64-inch drill bit as a gauge.
Install the front metering block-to-fuel bowl gasket onto the metering block. Again, register the gasket onto the locating pins on the metering block. The secondary-side metering plate on a 4160 installs independently to the main body with 8-32 x 1/2–inch clutch-head screws torqued to 12 to 18 in-lbs. It fastens to the main body separately; it is not held in place by the secondary fuel bowl.
Step 1: Inspect Locating Pins (Critical Inspection)
The locating pins on the rear of the metering block are close to the sides of the block. The two small locating pins on the metering block register into two small pin holes in the face of the main body.
Step 2: Inspect Locating Pins CONTINUED
Step 3: Install Air-Mixture Needle in Metering Block
Be sure to install a new cork-rubber gasket in the metering block’s mixture-screw port. Lightly lubricate the mixture screw and begin thread engagement by hand. Be careful to avoid cross threading. Continue to gently tighten the mixture screw with a small flat-blade screwdriver until it just bottoms-out, and then back it out about 11 ⁄2 turns.
Step 4: Install Gasket on Metering Block
Step 5: Install Gasket on Metering Block (CONTINUED)
Install a new front gasket onto the face of the metering block, registering the nine holes in the gasket to the nine locating pins on the front of the block. Place the metering block onto the main body; make sure that the rear gasket remains registered to the block. Do not apply any adhesive to either gasket.
To make registering it with the main body a bit easier, and avoid having the gaskets slip out of position, hold the block with the mating deck upright (vertical). Hold the metering block in place to prevent it from accidentally dropping off the main body. The metering block does not screw onto the main body. It is sandwiched in place, between the main body and fuel bowl, with the four fuel-bowl screws.
Fuel Bowl Installation
Install a new nylon gasket onto each fuel-bowl screw. With the metering block positioned on the main body, place the fuel bowl onto the metering block while lifting the accelerator pump throttle linkage (to allow the accelerator pump arm to contact the underside of the throttle arm). Insert the four 12-24 fuel-bowl screws and finger-tighten to engage the threads.
When all four screws are engaged to the female threads in the main body, keep the fuel bowl against the metering block and tighten the four bowl screws; torque to 25 to 30 in-lbs, using a crisscross pattern. When adjusting the accelerator pump arm contact, fine-tune the length of the spring-loaded adjuster bolt until you have zero clearance between the adjustable spring contact linkage and the pump lever at closed throttle.
Then, move the throttle linkage to WOT. At WOT, use a feeler gauge to make sure that you have about .015-inch clearance for additional travel of the diaphragm lever.
Carbs with an External Fuel Transfer Tube
Some carbs, such as Series 4160 (PN 1850), have an external fuel transfer tube that connects the front fuel bowl to the rear fuel bowl. A rubber seal at each end of the transfer tube seals the tube to the fuel bowl.
Discharge Nozzle Installation
When installing a discharge nozzle, be aware that the small accelerator check-valve pin must be dropped into the nozzle well first and that it uses two small gaskets. Using a hemostat when handling small components, such as placing the pin and the gaskets, is extremely helpful. Place a drop of lubricant, such as Vaseline, onto the lower gasket to help hold it in place. When placing the discharge nozzle, make sure that the notched area engages with the guide tang before attempting to tighten the nozzle’s mounting screw.
Step 1: Install Accelerator Check-Valve Pin
Before installing the discharge nozzle, remember to reinstall the accelerator check-valve pin. Drop the pin into the discharge passage with the pointed end down. This pin is being placed into the secondary side.
To ease handling and installation of the very small accelerator check-valve pin in the primary side of a carb that’s equipped with a choke plate, it’s helpful to secure the pin with a hemostat because the access is fairly tight. Locate the tip of the pin into the discharge passage and then carefully release the hemostat’s grip, allowing the pin to drop into place.
Step 2: Install Discharge Nozzle
Before installing the discharge nozzle, make sure that the nozzle and its mounting screw are clean. Always use a new lower gasket and new upper metal washer. When the screw is tightened, the metal washer deforms into a concave shape to seal the countersunk mating between the screw head and the top of the discharge nozzle.
Apply a light coating of lube, such as Vaseline, to the discharge nozzle’s lower gasket and place the gasket onto the bottom of the nozzle. This eases installation and helps to prevent the gasket from slipping. Position the upper metal washer over the screw and then install the screw; tighten it to 30 to 50 in-lbs. Make sure that the center notch on the discharge nozzle body seats into the small pocket on the main body
A choke mechanism incorporates a plate that closes over the primary side to create a stronger vacuum signal to restrict air and allow a richer fuel mixture to help a cold engine start. The choke plate remains closed or nearly closed to increase fuel atomization until the engine warms up. This vacuum-assisted choke also has a rubber diaphragm that opens the choke a little as engine vacuum begins to develop when the engine starts; it helps to prevent an over-rich condition. The choke plate works in tandem with a fast-idle cam that increases engine speed during this warm-up period. Most Holley carbs with a choke use either a mechanical or an electric choke. The mechanical choke is controlled directly by the driver via a cable. The electric choke is fitted with a thermostatic spring inside a housing; careful adjustment provides dependable cold-engine starts.
Manual Choke Installation
Step 1: Install Choke Housing
Before installing the choke housing, rotate the spring-loaded choke arm so that the small arm rests against the actuator pin (shown). As you install the housing into the main body, the hole in the long arm must engage onto the choke-plate rod.
Secure the choke-housing screws to the main body, making sure that the choke-plate rod is engaged in the lever arm. Torque the screws to 6 in-lbs.
Step 2: Install Cotter Pin on Choke Rod
Using a hemostat to install the hairpin clip is advisable because there probably isn’t enough access for your fingers.
Install the hairpin clip onto the choke-plate rod.
Electric Choke Installation
Step 1: Install Electric Choke Assembly
A vacuum port is at the rear of the electric choke housing. Be sure to install a new cork-rubber gasket.
Install a new gasket between the electric choke housing and cap.
Step 2: Install Electric Choke Assembly (CONTINUED)
Install the spring washer onto the choke cap and lightly secure the three mounting screws in the cap.
Step 3: Adjust Choke Assembly
Vacuum Secondary Installation
The vacuum secondary system contains a vacuum housing with a rubber diaphragm and spring. It’s important to use care during assembly to prevent distorting the diaphragm, which will cause an immediate vacuum leak and inoperative secondary actuation. Assembly is a bit easier if the housing is held upside-down while installing the spring, diaphragm, and housing cover.
Step 1: Install Vacuum Secondary Diaphragm
It may be difficult to avoid a vacuum leak while installing the secondary diaphragm into its housing. Try to avoid installing the diaphragm while the rubber is “tulip” shaped; it is difficult to seat the rubber properly.
Push the rubber into its proper shape, with the gasket surface flat where it contacts the housing. This helps to flatten out the rubber.
Notice the small vacuum orifice at the upper right. The captured hole in the gasket must align with this orifice.
Step 2: Install Accelerator Pump Gasket
Push the diaphragm into the cap while you hold the cap, spring, and diaphragm upside-down on a flat surface (this keeps the rubber flat). While holding the cap and diaphragm, slip the housing over the rod and onto the rubber, aligning the screw notches of the gasket to the screw holes in the cap and housing. It’s a bit tricky, but be patient; you’ll get it.
Step 3: Install Gasket into Vacuum Port
With the cap secured by the four screws, examine its perimeter to see if the gasket has pushed out. If all looks good, you can perform a vacuum check. Be sure to install a new cork-rubber gasket in the vacuum port.
Step 4: Seat Rod in Secondary Vacuum Assembly (Important!)
While holding a finger over the vacuum port, push the rod into the housing until it is fully seated; release the rod while still plugging the vacuum port. If the rod drops freely, you have a vacuum leak and must re-position the diaphragm.
Step 5: Install Secondary Vacuum Assembly
Step 6: Install Secondary Vacuum Rod onto Pivot Lever
Step 7: Install C-Clip over Pivot Lever
Install the tiny C-clip to secure the bottom of the operating rod; using a hemostat can make this a bit easier. The clip is very small, so be sure to handle it over a clean work surface in case you drop it. Verify that the C-clip is fully seated in its groove.
Throttle Plate Installation
The following is an overview of the procedure for installing a throttle plate.
Step 1: With the throttle-plate screw holes aligned with the shaft, install the screws. Add one drop of Loctite 290 to each screw thread. Snug down both screws, and then back them out half a turn. Lightly open and close the throttle. Do this at least six times so the plate can seat in the throttle bore.
Step 2: Tighten the screws. Open and close again to check for binding. If any binding is present, repeat Step 1. If there is no binding, repeat with the next throttle bore.
Step 3: After the new throttle plates are installed, open the throttle to wide open and release. Do this as fast as possible at least 10 times. Be absolutely sure that there is no binding present. Repeat all steps if necessary.
Secondary Metering Plate Installation
A secondary metering plate (used on the secondary side of 4160 carbs) has drilled restrictions rather than a metering block that has replaceable jets. Holley offers a wide range of metering plates for tuning 4160 carburetors.
Holley secondary metering plates are secured to the main body with six 8-32 x 1/2–inch flat-top screws that feature clutch-head drive; use a 5/32-inch clutch-head driver. In a pinch, you can use a small flatblade screwdriver of the appropriate size, but it’s not recommended. Clutch-head driver bits are readily available, and they’re cheap (approximately $1.50 each).
A better choice is a full-handled clutch-head driver, such as NAPA Auto Parts’ version (PN M-135). Clutch-head screws are used because the drive style is positive and not prone to stripping out, as long as you use a clutch-head tool.
You can replace the clutch-head screws with the “Phillips” style. If you do, be sure you use size 8-32 x 1/2– inch, in the flat-top design (flat-head face and countersink under-head). I prefer to use the style Holley uses, but some Demon carb metering plates are secured with Phillips-style screws, so either works. Sets of new clutch-head screws along with plate and bowl gaskets are available as a kit if you destroy or lose any of the original screws.
Carburetor mounting studs have 5/16-18 threads for intake manifold engagement. Most aftermarket carb studs have 5/16-18 threads on the lower section and 5/16-24 upper threads for nut engagement. Carb studs should be hand-snugged to the intake manifold. Torque the nuts only to 60 to 80 in-lbs. Do not overtighten the studs to the manifold. Although you may be tempted to “double-nut” the studs to tighten them to the intake manifold, avoid doing so. Overtightening the studs to the manifold can result in slight splaying. Only apply the torque value to the nuts that engage to the studs; do not torque the studs to the 60- to 80–in-lbs value.
Once the nuts are torqued to specification, the studs are secured. This is a common mistake among novices. Never excessively tighten any stud.
Written by Mike Mavrigian and Posted with Permission of CarTechBooks