[Tom Vaught]

A few more Engine and Carb tips that will apply to Holleys and other "clone" carbs.

1. Get Organized.

Make sure the ignition is working properly. Check timing (base, mechanical, and vacuum). Check plug gap, condition, and heat range. Check wires and make sure no two sequentially firing wires are routed side by side. Air and fuel filters should be clean. When possible, do tuning with air cleaner in place. Verify fuel pressure and install regulator if necessary. Inspect/replace vacuum lines. If you're working with a used Holley carb, when in doubt, rebuild it. Take your time and do it right the first time. Before disassembling, count the number of turns it takes to lightly seat the idle mixture screws. Also, make a sketch of the choke housing and linkage positions. Use these when you reassemble the carb. Disassemble and soak in mild carb cleaner. Rinse off thoroughly with Gasoline or Gumout Always wear proper eye protection, quality rubber gloves, and long sleeved clothing (shop coat, etc. . If the finish is not uniform, leave it alone. The Dichromate coating is what protects the carb inside and outside.

Check that all the surfaces are flat with a straight edge. Verify all the passages are clear by blowing through with air.

Use the proper rebuild kit. If you have an OEM application Holley, the local parts store books may not list the actual carb so you may need to contact Holley or Quickfuel for the proper rebuild kit part number. Closely compare the old parts with the new ones in the kit. Some of the kits have parts that don't quite seal or have slightly different threads and can cause problems. One thing to look out for is the power valve shoulder style. Some are beveled and some are flat If your original power valve shoulder is flat and you replace it with one with a beveled shoulder, it may leak. This can be difficult to diagnose because it will act just like a blown power valve but, when you inspect the valve, it will be fine. Some power valves have slightly DIFFERENT threads and can damage your METERING BLOCK threads when you tighten down the valve. Be careful when replacing the needle and seat assemblies. You can strip out the bowl threads if you over-tighten the locking screw or use a cheap imitation needle and seat assy. (Don't use the needles that have the screw slot cut in the top, with a lock nut that locks down the threads.) They are known for trashing bowls since the tendency is to over-tighten them. Use the original Holley style that has the large headed screw that goes into the needle, and the hex adjuster piece below it used to turn the needle assembly up and down. If you can't find them locally, they can be had directly from Quickfuel.

If you do a lot of carb work, use coated gaskets that don't stick when you disassemble the carb. Coating with chap-stick also works in a pinch. On old carb fuel bowls check that the little crimped on retainer on the bottom of the bowl accelerator pump cavity (holds the check ball in place) is not loose. Re-crimp or peen if necessary. Check floats for "no leaks" in the float and pre-set the float drop. Make sure secondary diaphragm is not torn and is properly positioned. With the carb fully assembled but still off car, fill the carb with fuel and check accelerator pump for a strong squirt. Do not use check balls, use only Holley Accelerator Pump Needles. Use black Permatex 300 (sparingly) on the little gaskets to hold in place and help sealing. Don't put high tension return springs on carbs, the main shaft bushings wear quickly that way.

Be careful on initial engine start-ups, watch for backfires (Keep a damp rag close by) to toss over the airhorn of the carb.
The flame will go out. It's easy to get the timing off during a engine rebuild and get some backfires.

If you are running a blow through carb setup, with a turbo or Supercharger, it is best to use a power valve plug till the basic starting and idle are adjusted. Once it starts and idles good, put the power valve back in.

Make sure carb throttle plates and the choke plate open fully. Check for manifold-to-head and manifold-to-carb vacuum leaks. If leaks are suspected, spray with the suspected leak location with Gumout or starting fluid (watch the paint). The engine should surge or stumble if there's a leak. Watch for fuel leaks. Some leakage from throttle shafts, when pumping the accelerator with the engine off, is normal. Soak it up before re-starting the engine. there should be no leaks when running.

Be alert to carburetor flooding when fuel is first applied. Flooding can be caused by dirt, small particles of hose cuttings, flecks of RTV, etc. If flooding is apparent, tap the body of the carburetor lightly with the wooden handle of a small hammer. If flooding continues, pinch the fuel line hose to shut off flow, run the engine to clear the carburetor, and let the fuel line flow again. If flooding still continues, disassemble and clean the carb.

Avoid extreme fuel pressure. At IDLE, there should not be any more than 7 psi; if the vehicle has an adjustable fuel-pressure regulator, set it to 6.0 psi. With most fuel pumps the minimum fuel pressure is encountered at high rpm and WOT. Fuel pressure should not drop below 3.0 psi. If it does, a fuel pump with more capacity may be required. Some mechanical pumps will give more than 6.0 psi at idle. The vehicle will perform well, but may be prone to stalls on quick turns and stops with the clutch disengaged. If this problem occurs, check the fuel pressure. If it is more than 7.0 psi at IDLE, it should be reduced through the use of a regulator. Always use a quality filter between the pump and carburetor. Note that a good filter is large in area, so it may be able to transmit a significant amount of heat to the fuel. It is a good practice to keep the filter away from heat and not allow it to come in contact with any part of the engine.

Air Cleaners: Your carburetor was originally calibrated with a low restriction open element air cleaner configuration. A 14 x3 unit is best for most. It will perform using a variety of other air cleaner designs and will perform as intended with nearly any reasonable air cleaner design. With a 14x3, the carburetor does not exhibit excessive sensitivity to the air cleaner, there are several guidelines you should follow when selecting an air cleaner: Running without an air cleaner is strongly discouraged for a street driven vehicle. Dirt and varnish will accumulate in critical bleeds and upset the fuel metering. Dirt and debris may easily get into the fuel bowl through the bowl vents or larger bleeds and cause a multitude of problems. Any calibration testing should be performed with the air cleaner in place. Depending upon the air cleaner used, the metering typically will be leaner with the air cleaner in place. A large 14"x3" open element air cleaner offers almost no resistance to air flow. Flow bench results show virtually no reduction in air flow. Also, this design should cause no change to the fuel metering. A 10"x2" open element design will result in some definite air flow restriction but little change to the fuel metering. Elements smaller than 10"x2" are more restrictive and have the most effect upon metering. If you have a dual-purpose vehicle that is sometimes used in competition without an air cleaner, it may be necessary to have two separate calibrations. DO NOT allow the vehicle air-stream to blow across the top of the carburetor(s) such as on an open-bodied car or full-bodied vehicle with a tunnel-ram manifold. The flow of air across the carburetor will result in an upset to the fuel metering that cannot be accommodated by recalibration since the change to the A/F Ratio will be different for every vehicle speed.

Have a great Super Bowl Sunday.

Tom V.