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Simple Tune-up Procedure

submitted by Ryan Bell (AKA: 69Bronco)

For those of you driving vintage iron, you are aware that your rig's performance will degrade over time if it is not properly maintained. In addition to general maintenance, routine tune-ups will increase performance and fuel economy. NOTE: Any kind of general tune-up information given here should be accompanied by the information contained in a good shop manual. Haynes sells automotive shop manuals for most of the vehicles still on the road today, and can be had for around $15 at most auto parts stores. Heed all information and warnings contained therein. This write-up is not intended to replace, but rather to supplement the procedures outlined in the shop manual. The information I am presenting has been gleaned by my own personal automotive work, almost exclusively on vintage Ford V8's. The techniques outlined here pertain to that type of engine, but the basic principles are generally similar among other makes and models. This information pertains to carbureted, pre-emissions, points-condenser ignition type engines. Modern fuel-injected engines, engines with emissions controls, and engines with electronic ignition have different operating principles and should be tuned up according to the shop manual procedure ONLY. Failure to do so could result in damage to your engine, or injury or death to you.

Parts Replacement and Diagnosis

A major tune-up generally involves replacing common wear components on an engine as well as setting up carburetor idle and mixture settings, and setting the ignition timing. This section deals with replacing components.

the patient

the operation seems to have been a success!

test results indicate patient will make a full recovery!


Air, oil, and fuel filters are the big three in this category. The air filter should be changed about every 12,000 miles, every other oil change, or whenever it is excessively dirty. A good rule of thumb is to change it when you can no longer easily see visible light though the filter element when held up to a light. The air filter on older vehicles is usually located in the stamped steel enclosure sitting atop the engine. Unscrew the wing nut holding it down, remove the top cover, and then remove the filter. Installation is reverse of removal. Oil filters should be replaced every oil change. Some manufacturers recommend that the filter need only be replaced every other oil change, but at less than $5, an oil filter is cheap insurance for your multi-thousand dollar engine. Oil should be changed every 3000 miles when on a severe-duty schedule, but under normal conditions oil will easily last for 6000 miles if it is of a good quality petroleum or synthetic motor oil. To change the oil, locate the drain plug on the bottom of the engine. With the engine off, remove the drain plug and allow the oil to drain into an appropriate receptacle so that it may be returned for recycling (at either an auto parts store, or local recycler).

Replace the drain plug. Now unscrew the oil filter either by hand (if you're strong enough) or with an oil filter wrench. In a pinch, you can skewer the oil filter with a sharp screwdriver and a hammer to wrestle it off if you lack a proper wrench. Be careful to catch any oil that may drain out. Now, take the new filter, and "prime" it with some fresh oil. Depending on mounting location, you may only want to fill it half full to prevent spillage during installation. Spread some fresh oil on the sealing o-ring on the filter, and screw it on to its mounting boss. Once the o-ring contacts the boss, tighten it ¼ turn more. Now simply refill the crankcase with the proper amount of engine oil, and that's done. Fuel filters on older vehicles are generally inline type filters. Often, it is a small 35mm film canister size device that screws onto the carburetor and it connected to the fuel line on its opposite end. Sometimes there can be another inline filter farther up the line. Some of these can be plastic. To renew these, simply unscrew any hose clamps, and unscrew the filter from the carburetor (if it is such a type), and replace it with the same type of filter. Installation is reverse of removal.

Distributor Cap

Checking under the distributor cap, one should look for signs of burnt terminals, arcing, cracking, or carbon tracking inside the cap. Any of these is good reason to renew the distributor cap. To replace the distributor cap, one at a time transfer the old wires onto the new cap's corresponding terminals. Be careful that the cap is in alignment with the old cap so as to prevent accidental wire mix-ups. Also mind that the new cap is held in correct orientation and not 180 degrees in reverse, as it only goes on one way. Many caps have the #1 cylinder terminal marked with a "1" stamped on the cap. This is usually a good starting point. Once all the wires are transferred over, remove the old cap by undoing the two clips that hold it in place, and discard it. The new cap may be left off for now, as it provides access to the points and condenser, which will be addressed in the next section.

Spark Plug Wires

If your rig is older, or it has been exposed to extreme conditions, its plug wires may have deteriorated. Replacing them is a simple way to improve performance as well as increase reliability. To replace plug wires, it is generally easiest to obtain a custom or semi-custom set from your auto parts store. ONE AT A TIME, simply remove the old plug wires, and replace them with new ones of corresponding length. Replacing them one at a time prevents accidentally mixing up the distributor terminals with their proper plugs. If you are using a one-size fits all kit, simply one at a time remove the old plug wires, measure it, and cut and crimp a new wire that matches the old one.

Spark Plugs

Spark plugs are not only an important part of your ignition system, but they can also tell you about the condition of your engine. A shop manual will usually give a guide for "reading plugs", but generally the ideal used plug looks light brown to tan. A very black, oily looking plug could be an indicator of more serious engine problems, and should be brought to the attention of a qualified mechanic. To replace spark plugs, one at a time remove the plug wire and unscrew the plug with a properly sized socket. Replace plugs with new equivalent plugs, being careful to start the plug in its bore by hand to prevent accidental cross threading. Once the plug contacts the base, follow the manufacturers tightening instructions. (Generally 1/8 turn more for tapered seat plugs, and ¼ turn more for gasket seat plugs)

Ignition Tune Up

If you have a rough running engine, and suspect that the carburetor might be at fault, you may want to skip ahead to the "Carburetor Tune Up" section first, then come back to this section later. Tuning up a vintage ignition consists of replacing/adjusting the points and condenser, and setting the initial timing.

Points and Condenser.

If in doubt, it is easiest to renew these now as they only cost a few dollars. First, carefully examine the points and rubbing block. If the rubbing block appears severely worn, the assistance of a qualified mechanic should be sought. The points themselves are easiest to examine when removed. They are held in place by small screws that if dropped into the distributor can be difficult or impossible to recover. BE CAREFUL and do NOT drop them. The wires attached to the points can be removed by loosening the nut on the points with an appropriate wrench. Open the points, and look at the contacts. Burned or pitted contacts are a sign of a faulty condenser. Renew both points and condenser if burning or pitting is noticed. If the contacts are uneven, or have high points, they should be filed off level. A fingernail file is handy for such an operation. Once a satisfactory set of points and a good condenser have been installed, the point gap must be set. Chevrolet engines use an external adjustment screw to set point gap and dwell with the engine running. Ford engines do not have such an adjustment, and the point gap needs to be set with the engine off. Remove the positive lead from the ignition coil, and use an external starter or a friend to bump the engine over until the points rubbing block is on one of the peaks of the rubbing block. Now, using a feeler gauge, open or close the points contact gap until only a slight drag is felt on the feeler gauge. The point gap should be 0.017" for most Ford engines. When the proper gap is set, tighten all the hold-down screws, recheck, and re-adjust point gap if necessary. Now you may reconnect the positive lead on the coil, and reinstall the distributor cap.

Ignition Timing

Ignition timing is set either by using a timing light (preferred) or "going by ear" to rotate the distributor to its ideal setting for ignition timing. The timing light method is outlined in the shop manual. Below is the "by ear" method. To set the timing by ear, first loosen the distributor hold down bolt, being careful not to disturb the distributor's rotation. With all vacuum advance controls hooked up, and with the engine running, slowly rotate the distributor and listen for a change in RPM. Generally, turning the distributor clockwise will advance the timing and increase RPM, while turning it counterclockwise will retard timing and decrease RPM. Turn the distributor until max RPM is found. Usually advancing timing beyond this point will cause the engine to stutter and/or stumble. After finding the max RPM setting, retard the timing slightly (about .25" movement of the vacuum advance canister on the distributor). This setting is the "max performance setting". Under heavy acceleration, or when using lower grades of gasoline, a slight knock may be audible. Retarding the timing a few more degrees will eliminate this problem. Should it be found that after a test drive there is a flat spot in the throttle under acceleration (not due to the carburetor), the timing may have to be backed off more. To determine if the flat spot is due to the carb or the timing, disconnect the vacuum advance line and plug it, then repeat the above timing procedure. If the flat spot still exists, it is due to the carburetor. When setting ignition timing, it may be necessary to "play with" the timing a bit to find your vehicle's "sweet spot". Once the timing has been set to your liking, be sure to re-tighten the distributor hold down after shutting down the engine.


This is a section all of its own because despite its simplicity, the carb can sometimes be a nightmare to set right. One way to become intimately familiar with your carburetor in a hurry is to rebuild it. Basic 2 barrel carburetors like the Motorcraft 2100 found on most small block ford engines is dirt simple in design and can be rebuilt fairly easily by anyone who can read directions and work with small parts. Additionally, rebuild kits are available for usually less than $20. The investment is worth the peace of mind that comes from having an intimate knowledge of how your rig works. If you do decide to rebuild your own carburetor, follow the directions that come with the rebuild kit TO THE LETTER. Since every carburetor is different, I will leave it to you to follow the directions yourself. Also, it would be wise to invest in a magnetic parts tray to keep the smaller parts from rolling away (there are some itty bitty springs and such in there!).
Now that you have your carburetor in good running shape, it's time to tune it.

NOTE: the following information is paraphrased from the Edelbrock Performer Series Carburetor owner's manual. Copyright 1993, Edelbrock. Instructions are not taken directly out of the manual, but the general guidelines are adhered to.

Automatic Choke

Many carburetor problems such as rough running can be attributed to an ill adjusted automatic choke. (Manual choke carburetors exempt, of course). On an electric choke carburetor, how long it takes for the choke to fully open is controlled by rotating the plastic "choke cap". Run the engine to normal operating temperature, and with the engine running rotate the choke cap until the choke is fully open. Now, slowly rotate the choke cap until the choke just begins to close. Lastly, rotate the choke cap back about 5 degrees in the "choke open" direction, and tighten the retaining screws. The automatic choke should be adjusted like this periodically as temperatures change though out the year.

Idle Speed and Mixture

This step requires the use of a tachometer. Additionally, the tachometer must be a fairly sensitive shop-type that will show differences as small as 25 or 50 rpm, or you will need a sensitive ear. You will also need to locate the idle adjustment screw (IAS), and the two idle mixture screws (IMS). The IAS is usually located so that it acts on the throttle linkage at the carburetor. The IMSs are usually located on the front bottom of the carb, at a 45-degree angle; one on each side in line with the venturi bores. Turning the IMSs clockwise (CW) will lean the idle mixture, while counter clockwise (CCW) will enrich the mixture. After fully warming the engine and ensuring the choke is open and the air cleaner in place, set the desired idle speed with the IAS (usually between 500-1000 rpm, depending on auto or manual trans). Next, adjust the IMS on ONE side to get max rpm. Do not go rich beyond max rpm. If the idle speed changed more than 40 rpm, go back and reset the IAS. Adjust the other IMS to get max rpm. Reset the IAS to desired idle. Carefully trim each IMS again to get max RPM at idle. Now, go leaner just enough to get a 20 RPM drop. Reset the IAS, and your carburetor is now tuned to the Lean-Best Idle Setting. Going richer beyond this point has no advantages, and will only tend to foul plugs.

Accelerator Pump Calibration

If any hesitations or stumbles are encountered that do not seem related to the basic fuel metering of the carburetor or to the ignition, you might want to play with the accelerator pump. Moving the pump drive link to a hole closer to the carb body will result in a longer pump stroke that delivers more fuel, while moving the drive link to a hole farther away will result in a shorter stroke with less fuel delivered. Trial and error is the best method for this adjustment. Set it to your own personal preferences.

Carb Float Adjustment

After removing the top air horn of the carb, you can check the float adjustment. Exact figures and procedures are available in the shop manual, but generally 7/16" of float drop (measured from the top of the float to the machined top surface of the carb body) is standard in Ford carbs. When adjusting the float, be sure not to force the needle into its seat during the bending process, as this will damage the needle and/or seat. For heavy off-road use, spring-loaded needle and seat assemblies are available, and the float drop should be re-adjusted to 3/8".

Jetting Adjustments

Cruise fuel mixture is controlled with brass "jets" in the carburetor. They can generally be removed with just a flat-tip screwdriver. Refer to your carburetor's shop manual for information on jetting changes for altitude.