I also find it best practice to return the carb to factory spec. when I'm dealing with an unknown.
from holley:
The use of a quality in line fuel filter, such as Holley P/N 162-523 is mandatory as a safeguard against possible flooding, which could result from unfiltered particles becoming lodged between the fuel inlet needle and its seat. This can result in fire if a spark is present or backfire occurs in the engine compartment. Air cleaner filter elements should be blown clean with compressed air at 6,000 miles and replaced at 12,000 miles to assure maximum protection. Now would be the perfect time to upgrade to a Holley Powershot air filter (Holley P/N 120-146). 7. Start the engine and check the fuel lines and inlet fitting for possible leaks. NOTE: The recommended fuel pressure is 5-7 psi. 8. Recheck to assure all existing vacuum hoses are attached properly. Plug any fittings not used. 9. With the engine at operating temperature, set the idle speed to the manufacturer’s specifications 10. If the carburetor is equipped with sight plugs, recheck fuel level with engine idling. 11. The accelerator pump should be adjusted so that the slightest movement of the throttle lever results in actuation of the accelerator pump. The pump override spring adjustment is checked while holding the throttle in the open position and the pump operating lever held in a fully compressed position. The clearance between the adjusting nut and the arm of the pump lever should be .015”. See figure 2 Figure 2—Accelerator Pump Adjustment Procedure 6 12. After making this adjustment, move the throttle lever from a closed position toward open. Any movement at the throttle lever should be noticed at the pump operating lever. This indicates correct tip-in. NOTE: Under no circumstances should the pump override spring be adjusted to permit coil bind (or bottoming). This is sometimes recommended by some “experts” as a means to a quicker delivery rate and increased flow. All that such “adjustments” accomplish is to provide bent accelerator pump actuating levers and ruptured pump diaphragms. Override springs are carefully sized to provide proper delivery pressure without damaging vital carburetor parts by momentarily absorbing pump force and regulating the pressure peaks within the system.
TUNING: Before you begin to tune your carburetor for your particular vehicle, you must get a “feel” for your vehicles performance so that any changes you make (good or bad) will be readily apparent. Be patient and make only one change at a time so only that change can be fully analyzed. This cannot be over emphasized as there are no “short-cuts” to peak performance. Recording each change and the resulting performance increase or decrease will provide you with a handbook of how vehicle performance is affected by individual carburetor adjustments. This may be helpful in the future or on other applications. IDLE MIXTURE NEEDLES Idle mixture needles control the air/fuel mixture at idle. When tuning the idle mixture, you’re actually tuning for the best manifold vacuum. Idle mixture needles are found on the primary metering blocks. If you change one idle mixture needle, you must change the other idle mixture needle by the same amount. Here are the proper steps for setting the idle mixture needles. 1. Attach a vacuum gauge to a manifold vacuum port on the throttle body. 2. Lightly seat the mixture screws by turning clockwise. Now turn them out 1.5 to 2 turns. This will give you a good starting point. 3. Adjust each idle mixture screw (Figures 3 & 4) 1/8 turn at a time, alternating between each screw. Turn them equally, until you achieve the highest possible vacuum reading without adjusting the curb idle speed screw. Turn screws in to lean the mixture. Turn them out to richen the mixture. 4. Now that the idle mixture is set, it may be necessary to go back and reset the idle speed using the curb idle speed screw. 5. If a vacuum gauge is not available, use a tachometer to obtain the highest RPM. Figure 3 Figure 4 7 ACCELERATOR PUMP The accelerator pump system consists of three main components: the pump diaphragm, the pump cam and the pump nozzle. This is the carburetor system that is most responsible for having good, crisp, off-idle throttle response. Its purpose is to inject a certain amount of fuel down the throttle bores when the throttle is opened. By accomplishing this purpose it acts to smooth the transition between the idle and main circuits so that no stumble, hesitation or sluggishness will be evident during this transition phase. NOTE: The old saying “if a little is good, a lot is better” does not apply to the proper tuning of the accelerator pump. Your car’s performance can be just as bad if it receives too much fuel as if it receives too little fuel. Two factors affect the accelerator pump’s delivery: First, The amount of fuel that can be delivered by one accelerator pump stroke. This is determined by the pump’s capacity and the profile of the pump cam. Secondly, the period of time that it will take for this pre-determined amount of fuel to be delivered. This is affected by the pump nozzle size. Pump Nozzle or “Shooter” A larger pump nozzle will allow this fuel to be delivered much sooner than a smaller pump nozzle. If you need more pump shot sooner, then a larger pump nozzle size is required. During acceleration tests, if you notice that the car first hesitates and then picks up, it’s a sure bet that the pump nozzle size should be increased. A backfire (lean condition) on acceleration also calls for a step up in pump nozzle size. Conversely, if off-idle acceleration does not feel crisp or clean, then the pump nozzle size may already be too large. In this case a smaller size is required. Holley accelerator pump nozzles are stamped with a number (Figure 5) which indicates the drilled pump hole size. For example, a pump nozzle stamped “35” is drilled .035". Pump nozzle sizes are available from .025" to .052". Please note that whenever a .040" or larger accelerator pump nozzle is installed the “hollow” pump nozzle screw should also be used. This screw will allow more fuel to flow to the pump nozzle, assuring that the pump nozzle itself will be the limiting restriction in the accelerator pump fuel supply system. NOTE: When changing the pump nozzle it’s best to jump three sizes. For example, if there is currently an off-line hesitation with #28 (.028”) pump nozzle, try a #31 (.031”) pump nozzle. Figure 5: Accelerator pump discharge nozzles are changed by removing a large Phillips hold down screw. NOTE: There is a small gasket under the head of the screw and one between the nozzle casting and the main body. 8 Figure 6: Accelerator pump cams are held in place with this small slotted screw. The pump lever should operate instantly with the slightest throttle rotation when cam is properly installed. Pump Cams Once a pump nozzle size selection has been made the accelerator pump system can be further tailored with the pump cam. Holley offers an assortment of different pump cams, each with uniquely different lift and duration profiles that are available under Holley P/N 20-12. Switching cams will directly affect the movement of the accelerator pump lever and, subsequently, the amount of fuel available at the pump nozzle. Lay out the pump cams side by side and note the profile differences. This little exercise may help to better explain the differences between the cams and their effect on pump action. Installing a pump cam is straightforward (Figure 6). It’s a simple matter of loosening one screw, placing the new pump cam next to the throttle lever and tightening it up. There are two and sometimes three holes in each pump cam, numbered 1, 2 and 3. Placing the screw in position #1 activates the accelerator pump a little early, allowing full use of the pump’s capacity. Generally, vehicles which normally run at lower idle speeds (600 or 700 RPM) find this position more useful because they can have a good pump shot available coming right off this relatively low idle. Positions #2 and #3 delay the pump action, relatively speaking. These two cam positions are good for engines that idle around 1000 RPM and above. Repositioning the cam in this way makes allowance for the extra throttle rotation required to maintain the relatively higher idle setting. Pump arm adjustment and clearance should be checked and verified each and every time the pump cam and/or pump cam position is changed.
JETTING (MAIN JETS): Due to varied applications that a universal performance carburetor will work with, no jets have been included in this kit; however a few tips on jetting are provided to help you understand their purpose. 1. Out of the box jetting is extremely close for most applications. 2. Carburetors are calibrated at 70° at sea level. Decrease the jet size primary and secondary, one number for every 2000 ft. increase in altitude. 3. Holley jets are broached, flowed, and stamped according to flow rate. NEVER drill jets, as this seriously alters flow characteristics. Stamped numbers are reference numbers and DO NOT indicate drill size. 4. In most cases it will be unnecessary to increase jet size more than four numbers greater than out of the box jetting. Exceptions could arise when the carburetor is mounted on a very large volume, plenum-ram manifold. 5. Spark plugs provide the best indication of proper jetting. Consult an ignition manual for proper reading of spark plugs.
POWER VALVES: The number stamped on a power valve, such as 65, indicates the manifold vacuum below which the power valve is operational. In this case, all manifold vacuums below 6.5” Hg, the power valve is operating. Generally a 65 power valve is sufficient for most high performance applications that have a manifold vacuum of 12” Hg or higher. However, some problems can result with radically cammed engines equipped with automatic transmissions. These vehicles often “idle” at 2000 rpm, approx. 6.0” Hg. At this point the main nozzles are starting to feed and richen the mixture (supplied by the power valve) and the engine will probably “load up”. To correct this problem, install a 45 or 35 power valve. If the engine has a manifold vacuum of 12” Hg or less, a good way to determine power valve size is take the manifold vacuum at idle and divide that number by two. The answer is the power valve size. This will provide idling and proper fuel flow under wide open throttle conditions when manifold vacuums seldom rise above 1” Hg. 11 AIR BLEEDS: Experimenting with air bleeds is not recommended. Countless hours of testing on expensive flow stands is required to obtain the proper bleed sizes for a given calibration. It is unlikely that a better bleed combination can be obtained without extensive experience and facilities. JET EXTENSIONS: Jet extension (Holley P/N 122-5000) can be used in conjunction with the secondary main jets to prevent the jets from being uncovered as fuel rushes to the back of the fuel bowl during extreme acceleration. Jet extensions require the use of a notched float. If you do not have a notched float, a notched float with jet extension is available as Holley P/N 116-10
Recommended fuel pressure: 7-1/2 psi maximum 5 psi minimum NOTE: Fuel pressures above 7-1/2 psi can create severe fuel control problems and are not recommended.
