Air/Fuel Mixture: Adjustments
Fig.38 Propane Enrichment Tool:
This procedure should only be used after normal diagnosis has revealed no other faults, or if carburetor has been overhauled. Idle mixture adjustment requires artificial propane enrichment. A propane enrichment tool, C-4464 or equivalent, Fig. 38, must be used to adjust idle mixture. Before proceeding, make sure that propane cylinder is adequately filled to insure correct propane flow.
Air cleaner must remain in place and A/C control must be in off position, except where noted. Disconnect and plug vacuum hoses at EGR valve and distributor, and control hose at vapor canister.
Holley Carburetors
1. Remove carburetor from engine and remove throttle body from carburetor.
2. Clamp throttle body in vise with mixture screws facing up. Make sure that vise jaws do not damage gasket surfaces.
3. On 1981 models:
Fig.42 Concealment Plug Removal (Typical):
a. Drill a 5/64 inch pilot hole in casting around each mixture screw, directly above limiter pin, Fig. 42, then enlarge hole to 1/8 inch.
b. Drive out pins with a suitable punch.
4. Drill a 5/64 inch pilot hole on manifold side of casting around each mixture screw, Fig. 42, at a 45° angle toward concealment plug, then enlarge hole to 1/8 inch.
5. Drive out concealment plugs with a blunt punch.
6. On 1981 models, insert a new limiter pin, allowing clearance for mixture adjustment.
7. Reassemble and install carburetor, using new gaskets.
8. Connect tachometer to engine following manufacturer's instructions. Start engine and run at fast idle until it reaches normal operating temperature.
9. Return engine to idle and place transmission in neutral.
NOTE: Ignition timing must be within specifications before proceeding with adjustments.
1O. Disconnect vacuum hose from heated air door at vacuum source and connect propane supply hose from metering valve on enrichment tool to fitting.
NOTE: Make sure that propane cylinder remains upright during adjustments.
11. Remove PCV valve from valve cover, leaving valve open to atmosphere.
12. Open main propane valve fully, then slowly open propane metering valve to obtain maximum idle RPM.
NOTE: Too much propane will cause RPM drop. "Fine tune" metering valve to obtain maximum RPM.
Fig.43 Propane Enrichment Adjustment Specifications:
13. With propane flowing, adjust idle speed to specified enriched RPM, Fig. 43 with curb idle speed screw.
14. Repeat steps 12 and 13, then turn main propane valve off. RPM should drop.
15. Allow engine to stabilize. Adjust mixture screws in small increments to obtain specified curb idle speed, allowing time between adjustments for engine to stabilize.
NOTE: Adjust mixture screws equally on 2 barrel carburetors.
16. With engine at specified curb idle speed, repeat step 12. If engine speed is more than 25 RPM different than specified enriched RPM, repeat steps 12-15.
17. Turn off both propane valves, remove enrichment tool an connect heated air door hose to fitting.
18. Adjust Electronic Throttle Control (1981) or Solenoid Idle Stop (1982), if equipped:
Fig.41 Throttle Solenoid (Typical):
a. Remove curb idle speed screw "A" and spring, Fig. 41.
b. On all 1981 models and 1982 models without A/C, separate wiring harness connector to solenoid and energize solenoid by applying battery voltage to proper terminal on solenoid connector.
c. On 1982 models with A/C, disconnect wiring harness connector to A/C compressor and place A/C control in on position.
d. Momentarily open throttle to allow solenoid plunger to extend.
e. Insert a 1/8 inch allen wrench into solenoid and adjust solenoid idle speed to specifications.
f. Remove jumper wire and connect wiring harness connector to solenoid (1981), or place A/C control in off position and connect wiring harness connector to compressor.
g. Reinstall curb idle speed screw and adjust curb idle speed to specifications.
19. Reinstall PCV valve and connect vacuum hoses to proper fittings.
NOTE: Engine idle speed may change, but do not reset.
Carter Thermo Quad Carburetors
1. Remove carburetor from engine and clamp in a suitable fixture with mixture screws facing up.
Fig.44 Concealment Plug Removal:
2. Drill a 5/64 inch pilot hole in side of casting around each mixture screw at a 45° angle toward concealment plugs, Fig. 44, then redrill hole to 1/8 inch.
3. Drive out concealment plugs with a blunt punch.
4. On 1981 models, insert a sharp punch through mixture screw access holes and remove limiter pins. Position new pins in bottom of throttle body allowing clearance for mixture adjustment.
5. Reinstall carburetor on engine, using a new base gasket.
6. Connect tachometer to engine following manufacturer's instructions. Start engine and run at fast idle until it reaches normal operating temperature.
7. Return engine to idle and place transmission in neutral.
8. On 1982 models, disconnect and plug vacuum hose at OSAC valve, remove air cleaner, and plug related vacuum fittings.
9. Disconnect vacuum hose to bowl vent at carburetor fitting and install a "T" fitting between hose and carburetor.
10. Connect propane supply hose from metering valve on enrichment tool to "T" fitting in vent hose.
NOTE: Make sure that propane cylinder remains upright during adjustments.
11. Remove PCV valve from valve cover, leaving valve open to atmosphere.
12. Open main propane valve fully, then slowly open propane metering valve to obtain maximum idle RPM.
NOTE: Too much propane will cause RPM to drop. "Fine tune" metering valve to obtain maximum RPM.
Fig.43 Propane Enrichment Adjustment Specifications:
13. With propane flowing, adjust idle speed to specified enriched RPM, Fig. 43, with curb idle speed screw.
14. Repeat steps 12-13, then turn main propane valve off. RPM should drop.
15. Allow engine to stabilize, then adjust mixture screws equally, in small increments, to obtain specified curb idle speed, allowing time between adjustments for engine to stabilize.
16. With engine at specified curb idle speed, repeat step 12. If engine speed is more than 25 PM different than specified enriched RPM, repeat steps 12-15.
17. Turn off both propane valves, remove enrichment tool and "T" fitting from vent hose, and connect vent hose.
18. On 1981 models, adjust Electronic Throttle Control:
a. Separate wiring harness connector to solenoid and energize solenoid by connecting battery voltage to solenoid blue wire connector.
b. Momentarily open throttle to allow solenoid plunger to extend.
Fig.40 Throttle Solenoid (Typical):
c. Adjust solenoid idle speed to specifications with screw "B", Fig. 40, then disconnect jumper wire.
19. Reinstall PCV valve and connect vacuum hoses to proper fittings.
NOTE: Engine idle speed may change, but do not reset.