Article 965 - IMCO and Thermactor Exhaust Emission Systems

TSB #965 - December 9, 1966
(1967 California Engines - 170, 200 and 289 [2-V] C.I.D.)


Two types of exhaust emission systems, Thermactor and Imco, are used on 1967 cars for California registration. The Thermactor system is the same as previously described in car shop manuals and Technical Service Bulletins. The Imco (Improved Combustion System) engines utilize revised valve timing events and different distributor and carburetor calibration. This improves engine combustion sufficiently to maintain the exhaust system contaminants at an acceptable level.

170 and 200 C.I.D. Engines
Early production engines in Falcon, Fairlane and Mustang Cars use the Thermactor system for both standard and automatic transmissions. Later production cars retain the Thermactor system for standard transmissions, while the Imco system is used on cars with automatic transmissions.

All Imco engines have a Carter 1-V carburetor, model YF, and do not have a coolant-heated carburetor spacer. The Autolite 1-V carburetor is used on these engines for other than California registration.

Other parts revised for Imco engine use only, are as follows: cylinder head, camshaft, exhaust manifold, coolant thermostat (higher operating temperature), distributor, air cleaner, radiator and cooling fan. The initial ignition timing, 170-3° and 200-5°, for Imco engines must not be used for Thermactor engines, and conversely, the Thermactor ignition timing must not be used for Imco engines. For service specifications, including carburetor and distributor, refer to TSB article 966. Refer to the Master Parts Catalog for interchangeability of parts.

Repair and adjustment procedures for the Carter YF carburetor are included in this article.

289 C.I.D. Engine
All 289 V-8 engines use the Thermactor exhaust emission system. However late production engines (except Bronco and Econoline) with a 2-V carburetor and with automatic transmission have been changed as follows:
    Increased the camshaft intake valve lobe lift;
    Increased the valve spring rate;
    Increased the radiator width;
    Increased cooling fan diameter and/or blade pitch;
    Changed the crankshaft, water pump and Thermactor air supply pump pulley diameters and the fan belt length.
On the late production engines only the new camshaft and valve spring may be used. The new valve spring may be used for service replacement of the early production valve spring. For interchangeability of all parts, refer to the Master parts Catalog. The new valve spring is identified by light green paint or by the pressure at specified length specifications. The camshaft is identified by cast-in letters VY between the rear lobe and bearing journal. All other parts are marked with part number prefix and suffix. Refer to TSB article 966 for service specifications.

The distributor and carburetor part numbers and service specifications are in TSB article 966. The initial ignition timing for late production 289 V-8 engines with Thermactor must be set according to the distributor part number or engine change level code (on engine identification tag) as follows:

Distributor Part No.Engine
Model
Initial
Ignition
Timing
Engine Change
Level Code
C7AF-AH289-2V6° BTDC15


CARTER MODEL YF CARBURETOR
DESCRIPTION
The carburetor that is used on 170 and 200 CID improved combustion (IMCO) system equipped engines is a model YF, a sing-venturi Carter Carburetor.

Image
Illus. B2964-A
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Illus. B2965-A
Image
Illus. B2954-A


The fuel inlet system is float controlled. A metal float and cushioned, 2-piece needle and spring are used. The inlet needle seat is replaceable. The fuel bowl is vented by a tube that connects the fuel bowl with the inside of the air horn. Some external venting is accomplished through the pump lifter link slot in the main body casting.

The idle and low engine speed fuel system consists of a low speed jet, idle fuel passages, idle passage re-strictor, idle air bleeds, and an adjustable idle needle valve.

An accelerating pump system that is diaphragm operated is located in the bottom of the fuel bowl. A ball inlet check valve and a needle-type outlet valve control the fuel passing into and out of the accelerating pump system.

Mid range and high speed fuel and air mixture is metered by the main metering system. This system consists of a main metering jet, metering rod, actuating linkage, a vacuum diaphragm, main discharge tube, air bleed, main and booster Venturis and a throttle valve. The carburetor has no power valve as such but the vacuum diaphragm spring will raise the metering rod out of its jet during high throttle openings.

The carburetor uses an automatic choke that is sensitive to air temperature. A bi-metal spring controls the position of the choke plate and choke linkage depending on the temperature of the air in the thermostatic coil choke housing. The air entering the coil housing is heated by exhaust manifold heat. A fast idle cam holds the throttle open slightly until the engine is warm.

Machined passages and fittings are provided for vacuum routing to the engine ignition distributor and for automatic transmission or accessory operation.

CARBURETOR REMOVAL AND INSTALLATION
Removal
    1. Remove the air cleaner. Disconnect the distributor vacuum line from the carburetor and the automatic transmission or accessory vacuum line if so equipped. Disconnect the automatic choke heat tube at the thermostatic coil (choke) housing on the carburetor. Disconnect the fuel line at the carburetor. Disconnect the accelerator linkage at the carburetor throttle shaft and lever assembly.
    2. Remove the two nuts retaining the carburetor to the carburetor adapter. Pull the carburetor straight up and off the adapter to prevent damage to the throttle plate.

Installation
    1. Clean all old gasket material from the carburetor throttle body flange and the carburetor adapter surface. Install a new carburetor to adapter gasket. Set the carburetor straight down on the adapter studs. Install the two retaining nuts and tighten evenly.
    2. Connect the accelerator linkage to the carburetor throttle lever. Connect the fuel line to the carburetor. Install the automatic choke heat tube to the thermostatic coil housing and tighten the tube nut. Connect the distributor and automatic transmission or accessory vacuum lines to the carburetor. Set the thermostatic coil housing index mark to specification.
    3. Start the engine and check for fuel or vacuum leaks. Allow the engine to reach normal operating temperature. Set the idle mixture and idle speed. Check and set the antistall clearance. Install the air cleaner, and reset the idle speed and mixture as necessary.

Image
Illus. B2966-A - Automatic Choke
Piston Removal or Installation
Image
Illus. B2967-A - Acceleration Pump
and Lifter Link Assembly
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Illus. B2968-A - Pump Diaphragm
and Housing Installation


CARBURETOR DISASSEMBLY AND ASSEMBLY

Disassembly
    1. Disengage the throttle connector rod retainer (Illus. B2954-A) from the choke connector rod, and pull the rod out of the fast idle link.
    2. Remove the attaching screws and retainers, the thermostatic coil housing assembly, coil housing gasket, coil housing baffle plate, choke trip lever and pin assembly, and fast idle link.
    3. Remove the air horn assembly attaching screws, dashpot and bracket assembly, air horn assembly, and air horn gasket.
    4. Hold the air horn assembly bottom side up, and remove the float pin and float and lever assembly. Turn the air horn assembly over and allow the needle pin, spring, needle, and seat to fall into the hand.
    5. Remove the needle seat and gasket.
    6. Remove the choke plate attaching screws. File the staked ends, if necessary, and use new screws upon reassembly. Remove the choke plate from the air horn assembly. Disengage the fast idle cam spring from the cam spring lever on the choke piston lever and shaft assembly. Rotate the choke shaft and piston assembly counterclockwise until the choke piston is out of the choke piston cylinder (Illus. B2966-A). Remove the assembly from the air horn. Remove the piston pin, piston, fast idle cam, and fast idle cam spring from the choke piston lever and shaft assembly.
    7. Turn the main body casting upside down and catch the accelerating pump check needle in your hand.
    8. Loosen the throttle shaft arm screw, and remove the arm and the pump connector link.
    9. Remove the accelerating pump diaphragm housing screws. Lift out the pump diaphragm assembly, the pump lifter link, the metering rod and the fuel bowl baffle plate as a unit (Illus. B2967-A).
    10. Disengage the metering rod arm spring from the metering rod, and remove the metering rod from the metering
    rod arm assembly. Compress the upper pump spring, and remove the spring retainer. Remove the upper spring, the metering rod arm assembly, and the pump lifter link from the pump diaphragm shaft. Compress the pump diaphragm spring, and remove the pump diaphragm spring retainer, spring, and pump diaphragm assembly from the pump diaphragm housing assembly.
    11. With the proper size jet tool or screwdriver remove the low speed jet (Illus. B2968-A).
    12. Remove the retaining screws and separate the throttle body flange assembly from the main body casting. Remove the body flange gasket.
    13. Remove the idle mixture screw and spring. Remove the throttle plate retaining screws. File the staked ends, if necessary, and use new screws upon reassembly. Slide the throttle shaft and lever assembly out of the throttle body flange assembly.

Cleaning, lnspection and Repair
The cleaning and inspection of only those parts not included in the carburetor overhaul repair kit are covered here. All gaskets and parts included in the repair kit should be installed when the carburetor is assembled and the old gaskets and parts should be discarded.

Wash all the carburetor parts (except the pump diaphragm and the antistall dashpot assembly in clean, commercial carburetor cleaning solvent. If a commercial solvent is not available, lacquer thinner or denatured alcohol may be used.

Rinse the part in kerosene to remove all traces of the cleaning solvent; then dry them with compressed air. Wipe all parts that can not be immersed in solvent with a clean, lint-free cloth. Be sure all dirt, gum, carbon, and other foreign matter are removed from all parts.

Force compressed air through all passages of the carburetor. Do not use a wire brush to clean any parts or a drill or wire to clean out any openings or passages in the carburetor. A drill or wire may enlarge the hole or passage, changing the calibration of the carburetor.

Check the throttle shaft and choke shaft for grooves, wear and excessive looseness or binding. Inspect the throttle plate and choke plate for nicked edges and for ease of operation and free it if necessary.

Make sure all carbon and foreign material has been removed from the automatic choke housing and the piston. Check the operation of the choke piston in the choke cylinder to make certain it has free movement.

Check the metallic float for leaks by holding it under water that has been heated to just below the boiling point. Bubbles will appear if there is a leak. If a float leaks, replace it.

Replace the float if the needle pin contact surface is grooved. If the float is serviceable, polish the needle pin contact surface with crocus cloth or steel wool. Replace the float pin if it is worn.

Replace all screws and nuts that have stripped threads. Replace all distorted or broken springs.

Inspect all gasket mating surfaces for nicks and burrs. Repair or replace any parts that have a damaged gasket surface.

Inspect the plunger rubber boot of the anti-stall dashpot for proper installation in the groove of the plunger. Check the plunger movement for smooth operation. Do not lubricate the plunger. Replace the assembly if it is defective.

Assembly
    1. Install the throttle shaft and lever assembly (Illus. B2954-A) in the throttle body flange. Position the throttle plate on the throttle shaft with the notch in the plate aligned with the slotted idle port (Illus. B2969-A) in the throttle body flange. Install the throttle plate attaching screws snug, but not tight. Move the shaft back and forth and rotate it to be sure the throttle plate does not bind in the flange bore. Reposition the plate if necessary. Tighten the screws and stake (or peen) the screws in place.
    2. Install the idle mixture screw and spring. Lightly seat the screw. Then back it out (unscrew) 1-1/4 turns for initial setting.
    3. Place a new body flange gasket and the main body casting on the throttle body flange. Install the attaching screws and tighten them evenly.
    4. With the proper size jet tool (or screwdriver) install the low speed jet and the metering rod jet (Illus. B2968-A).
    5. Install the pump diaphragm in the pump diaphragm housing (Illus. B2954-A). Position the pump diaphragm spring on the diaphragm shaft and housing assembly. Install the spring retainer. Install the pump lifter link, metering rod arm and spring assembly, and upper pump spring on the diaphragm shaft. Depress the spring and install the upper pump spring retainer.
    6. Install the metering rod on the metering rod arm and place the looped end of the metering rod arm spring on the metering rod as shown in Illus. B2967-A. Align the pump diaphragm with the diaphragm housing; make sure the holes are aligned. Install the housing attaching screws to keep the diaphragm and housing aligned.
    7. Position the fuel bowl baffle plate on the pump assembly as shown in Illus. B2967-A and B2968-A. Align the pump housing, pump lifter link, metering rod and baffle plate with the main body casting. Be sure the vacuum passage in the diaphragm housing is aligned with the vacuum passage in the main body. Install the assembly in the main body casting, being careful to engage the the pump lifter link with the main body, the baffle plate with the grooves in the main body, and to insert the metering rod in the metering rod jet. Install the pump housing attaching screws snug, but not tight. Push down on the diaphragm shaft to compress the diaphragm, and tighten the attaching screws. Adjust the metering rod, following the procedure under Metering Rod Adjustment.
    8. Install the throttle shaft arm and pump connector link on the throttle shaft and pump lifter link (Illus. B2970-A). Tighten the lock screw.
    9. Install the fast idle cam and spring on the choke piston lever and shaft assembly. Assemble the choke piston and pin to the choke piston lever and shaft assembly. Disengage the cam spring from the cam spring lever on the choke lever and shaft assembly. Install the choke shaft assembly in the air horn and position the piston as shown in Illus. B2966-A.
    10. Align the piston with the cylinder and rotate the shaft assembly clockwise until the piston pin is inside the piston cylinder. Position the cam spring on the cam spring lever of the choke lever assembly. NOTE: When the spring is properly positioned, the tangs on the cam and the choke lever will be aligned one in front of the other.
    11. Position the choke plate on the choke shaft and install the screws snug. Check the choke plate movement to be sure it isn't binding. Tighten the screws and peen or stake them to prevent loosening.
    12. Install the needle seat and gasket in the air horn. With the air horn inverted, install the needle, pin spring, needle pin, float and lever assembly, and float pin.
    13. Adjust the float level to specifications.
    14. Place the pump check needle in the main body casting (Illus. B2 968-A). Position a new air horn gasket, the air horn assembly, and the anti-stall dashpot and bracket on the main body. Install and tighten the attaching screws.
    15. Install the choke trip lever and fast idle link in the choke housing of the air horn. Be sure they are properly engaged with each other and with the choke piston lever and shaft assembly. Install the thermostatic coil housing, gasket and baffle plate with the gasket between the baffle and coil housing. Be sure the thermostatic spring engages the choke lever tang. Install the retainers and housing screws. Set the coil housing index to specifications and tighten the screws.
    16. Install the throttle connector rod retainer on the fast idle link. Install the choke connector rod on the throttle lever and fast idle link. Engage the connector rod retainer with the choke connector rod.

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Illus. B2969-A - Throttle
Plate Installation
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Illus. B2970-A - Throttle Shaft
Arm Installation
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Illus. B2971-A - Checking Float
Level Adjustment
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Illus. B2973-A - Anti-Stall
Dashpot Adjustment

ADJUSTMENTS

Float Level
    1. Remove the air cleaner.
    2. Disconnect the choke heat tube at the carburetor air horn. Disconnect the fuel inlet line at the carburetor,,
    3. Disengade the throttle connecting rod retainer from the choke connector rod, and pull the rod out of the fast idle link. Remove the air horn assembly attaching screws, dashpot and bracket assembly and air horn gasket. Discard gasket.
    4. Fabricate a float level gauge (Illus. B2971-A) to the specified float level dimension.
    5. Invert the air horn assembly, and check the clearance from the top of the float to the bottom of the air horn with the float level gauge (Illus. B2971-A). Hold the air horn at eye level when gauging the float level. The float arm (lever) should be resting on the needle pin. Bend the float arm as necessary to adjust the float level (clearance). Do not bend the tab at the end of the float arm, it prevents the float from striking the bottom of the fuel bowl when empty.
    6. Place a new air horn gasket on the carburetor main body casting. Install the air horn assembly, dashpot and bracket assembly and air horn attaching screws. Insert the end of the choke connector rod in the fast idle link, and secure it with the throttle connector rod retainer.
    7. Connect the fuel inlet line and choke heat tube to the carburetor air horn.
    8. Install the air cleaner. Start the engine and run it until normal operating temperature is reached. Adjust the idle fuel mixture and idle speed.

Idle Mixture and Speed
The engine idle speed is adjusted to settings for a hot engine and a cold engine (fast idle speed during choke operation), The fast idle (cold engine) speed setting on the Carter model YF carburetor is a bench adjustment (carburetor removed from engine). All final idle speed and mixture adjustments must be made on a hot, normalized engine.
    1. Operate the engine until engine temperatures are stabilized. On a car with air conditioner, operate the engine for twenty minutes before setting the engine idle speed. The engine idle speed is adjusted with air conditioner operating.
    2. Position the transmission lever in neutral. Allow the throttle to drop back to the normal idle speed position. Attach a tachometer to the engine. Set the parking brake.
    3. Turn on the headlamps. It is necessary to place the alternator under a load condition in this manner in order to obtain the specified engine idle speed during the adjustment procedure.
    4. On a car with a manual shift transmission, the engine idle speed is checked and adjusted with the gear shift lever in neutral position. On a car with an automatic transmission, the engine idle speed is checked and adjusted first with the transmission selector lever in the neutral position and adjusted with the transmission selector lever in the drive range position. Adjust and check the engine idle speed. Be sure the dash-pot (if so equipped) is not interfering with the throttle lever.
    5. Turn the idle mixture screw inward until the engine rpm begins to drop, due to the lean mixture. Turn the idle
    mixture screw outward until the rpm increases and begins to drop. Finally, turn the idle mixture screw inward approximately half way between the lean mixture and rich mixture settings.
    6. If the car is equipped with an automatic transmission, position the selector lever in drive range to check and adjust the idle speed to specification. Turn the idle speed adjusting screw inward or outward until the desired engine speed is obtained.
    7. Check and adjust the anti-stall dashpot.

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Illus. B2974-A - Choke Plate Clearance
(Pulldown) Adjustment
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Illus. B2972-A - Automatic Choke Thermostatic
Coil Housing Adjustment
Image
Illus. B2975-A - Fast Idle
Speed Adjustment
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Illus. B2976-A - Metering
Rod Adjustment


Anti-Stall Dashpot (Automatic Transmission)
The engine idle mixture speed must be properly adjusted before adjusting the anti-stall dashpot.
    1. Remove the air cleaner.
    2. Loosen the anti-stall dashpot lock nut (Illus. B2973-A).
    3. With the choke plate open, hold the throttle plate closed (idle position), and check the clearance between the throttle lever and dashpot plunger tip with a feeler gauge of the specified clearance dimension. Turn the dashpot inward or outward to obtain the specified clearance and tighten the locknut. The clearance must be measured with the plunger fully depressed.

Automatic Choke Plate Clearance (Pulldown)
This adjustment may be performed with the carburetor on or off the engine.
    1. Remove the air cleaner.
    2. Remove the thermostatic coil housing, gasket and baffle plate.
    3. Hold the throttle plate fully open and close the choke plate as far as possible without forcing it. Use a drill of the proper diameter to check the clearance between the choke plate and air horn (Illus. B2974-A).
    4. If the clearance is not within specification, adjust by bending the arm on the choke trip lever. Bending the arm downward will increase the clearance, and bending it upward will decrease the clearance. Always recheck the clearance after making any adjustment.
    5. Install the baffle plate, gasket and thermostatic coil housing. Be sure the thermostatic spring engages the tang on the choke lever and shaft assembly. Set the coil housing index mark to specifications and tighten the attaching screws.
    6. Install the air cleaner.

Automatic Choke Thermostatic Coil Housing Adjustment
The automatic choke has an adjustment to control its reaction to engine temperature. Turning the thermostatic coil housing in a counterclockwise direction requires a higher thermostatic spring temperature (cold weather operation) to fully open the choke plate. Turning the housing in the opposite direction (clockwise) causes the choke plate to be fully open at a lower thermostatic spring temperature (hot weather operation). This is the lean direction, as indicated by the arrow on the thermostatic coil housing. Refer to the specifications for the proper setting for normal ambient temperatures.
    1. Remove the air cleaner assembly.
    2. Loosen the thermostatic spring housing clamp retaining screws. Set the spring housing to the specified index mark (Illus. B2972-A), and tighten the clamp retaining screws.
    3. Install the air cleaner assembly.

Fast Idle (Cold Engine) Speed
The carburetor must be removed from the engine to check or correct the fast idle speed adjustment.
    1. Open the throttle plate and hold the choke plate fully closed to allow the fast idle cam (Illus. B2975-A) to revolve to the fast idle position.
    2. Close the throttle and use a drill with a diameter equal to the specified clearance to check the clearance between the throttle plate and throttle body bore (Illus. B2975-A). To adjust the clearance, bend the choke connector rod in a direction to open or close the throttle plate as required.

Metering Rod
    1. Remove the air cleaner.
    2. Disconnect the fuel line and choke heat tube at the air horn. Disconnect the choke connector rod from the fast
    idle link. Remove the air horn assembly, anti-stall dashpot and air horn gasket. Discard the gasket.
    3. With the throttle plate closed, press down on the end of the diaphragm shaft (Illus. B2976-A) until it bottoms in the vacuum chamber. Check the position of the metering rod. It should be touching the bottom of the metering rod well, and the metering rod arm should contact the lifter link at the lifting lug and at the diaphragm shaft.
    4. If necessary, bend the metering rod pin flange (on the metering rod arm) up or down to properly position the metering rod.
    5. Place a new air horn gasket on the main body, and install the air horn assembly and anti-stall dashpot. Connect the choke connector rod to the fast idle link, and secure it with the throttle connector rod retainer. Connect the fuel line and choke heat tube to the air horn.
    6. Install the air cleaner. Operate the engine and adjust the idle fuel mixture and speed as required.


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