When performing a tune up the ignition always comes first.
This month we will discuss that most mysterious of subjects, the carburetor. Most Cougars and Lincoln Mercury products used either the Autolite 2100 two barrel or model 4300 four barrel. I will try to be as specific as possible about these two units and get into aftermarket four barrels and factory Holley and Rochester carburetors in the future.
Proper installation and hookup is mandatory on either type carburetor. On the right (passenger) side of the engine should be a pair of tubes connecting the exhaust manifold to the carburetor. These do not inject exhaust or are they connected with the exhaust. The exhaust manifold has a built in chamber that heats air. This air is used to heat a thermostatic spring in the black choke housing. When the spring gets hot, the choke opens.
This sounds simple. It worked great 20-25 years ago when your car was new. It will work properly now with a little effort on the owner's part. The main problems with the system are:
- Somebody left the tubes off after the last valve job.
- The tubes o the chamber in the exhaust manifold are plugged
- You have tubular exhaust headers and no place to hook up.
The tube assemblies are available for under $25.00 from any of the major parts suppliers (Dallas Mustang or Mustang Parts Corral, etc.). The chamber in the exhaust manifold can usually be opened up by blowing compressed air into it while poking a piece of coat hanger wire down the top hole. Wear safety glasses!!
If you have exhaust headers the standard fix is to replace the stock tubing with a piece of copper tubing ¼ inch diameter. This can be neatly coiled around the tube from the #3 cylinder about three times and connected to the carburetor like the stock tubes. It is recommended to use asbestos insulation on the line leading to the center of the choke housing to prevent burning your spark plug wires.
Your choke must be adjusted when the engine is cold for any good results. My favorite choke adjusting days are about 40 degrees F with the car not operated for 12 hours previously. Loosen the three screws holding the clamp on the black plastic choke thermostat housing. With your left hand open the throttle slightly, not all the way. Then with your right hand adjust the choke thermostat so that the choke plate just closes. Release the throttle and tighten the three screws, remembering that 25 year old choke housings are very brittle, old plastic. Take note of the markings on the choke housing that say "Rich" and "Lean". Moving the housing towards "Rich" increases the spring tension closing of the choke and causes long periods of fast idle. Moving the housing towards "Lean" can decrease or even eliminate choke/fast idle all together.
On some carburetors a clamp is incorporated with the choke housing retainer that supports the heater hose. This is intended to keep the choke housing warmer and speed choke opening. Use it if you have it.
Your carburetor should have one fuel filter screwed into it with a short piece of rubber connecting hose. This filter should be changed every year or at tune up time. Cheap filters will get cheap results. Use a Motorcraft or Autolite for consistent quality. Caution: do not install inline filters between the fuel tank and the fuel pump. This is a common cause of vapor lock and can cause you to push your car into the left lane of Central Expressway during rush hour traffic. Filters should be installed between the fuel pump and the carburetor only. The stock filter will perform all the filtering you need if your fuel tank is clean.
The idle mixture screws on the lower front of the carburetor should be adjusted with the engine running. As a pre-adjustment, screw both mixture screws clockwise until they bottom gently. Do not tighten them more that "snug". Open each screw 1-½ turns. Start the car and adjust them counter-clockwise, ½ turn at a time, simultaneously. You're trying to achieve the fastest idle time speed. The screws must be open the same amount to preserve balance between both banks of the engine. The screws may be opened as much as (total) two turns each.
After setting the mixture screws adjust the main idle screw at the throttle linkage. This should be done with the headlights and air conditioning turned on.
