Idle Mixture, Adjust
Fig. 1 Propane enrichment specifications. 1983---84 Series 10-30/1500-2500 W/light duty emissions less C3:
Series 10-30/1500-3500 W/Light Duty Emissions Except 1983-87 Vehicles W/C3 System
Vehicles with a Gross Vehicle Weight Rating (GVWR) below 8500 lbs. are Light Duty Emissions Vehicles. Idle mixture adjustment requires artificial propane enrichment. Propane enrichment tool J-26911, or equivalent, is required to perform adjustments. Air cleaner must remain in place, and A/C control, if equipped, must be in off position except where noted.
1. Disconnect and plug vacuum hoses as directed by vehicle emission control label.
2. Connect tachometer to engine following manufacturer's instructions. Start engine and run at fast idle until it reaches normal operating temperature.
3. Place transmission in drive (manual transmission in neutral) and adjust curb idle speed to specifications.
4. Disconnect crankcase ventilation (PCV) tube from air cleaner. Insert hose with rubber stopper from propane valve into opening in air cleaner. Propane cylinder must remain upright during adjustments, and cylinder must be adequately filled to insure correct propane flow.
5. Slowly open propane metering valve while observing tachometer. Continue opening valve until engine RPM begins to drop and note maximum enriched RPM.
6. If enriched RPM is within specifications, Fig. 1, turn off propane flow and proceed to step 15.
7. If enriched RPM is not within specifications, turn off propane flow and remove plugs sealing idle mixture screws as outlined under ``Concealment Plug Removal'' in the appropriate carburetor section. On models with limiter caps, remove limiter cap from each mixture screw, taking care not to damage screws.
8. Start engine and allow it to reach normal operating temperature.
9. Turn each mixture screw in (clockwise) until lightly seated, then back screws out equally, just enough so engine will run.
10. Place transmission in drive (manual transmission in neutral).
11. Turn mixture screws counter-clockwise equally, 1/8 of a turn at a time, until maximum idle RPM is obtained.
12. Adjust idle speed to specified enriched RPM, Fig. 1, following procedure in step 3.
13. Turn mixture screws clockwise equally, 1/8 of a turn at a time, until specified curb idle speed is obtained.
14. Repeat step 5 then turn off propane flow. If enriched RPM is not within specifications, repeat steps 10-14.
15. If equipped with a throttle stop solenoid:
a. Disconnect wiring harness connector to solenoid.
b. Adjust low idle speed to specifications with throttle stop screw.
c. Reconnect wire to solenoid.
16. If equipped with an A/C speed-up solenoid:
a. Disconnect wiring harness connector to A/C compressor and place A/C control in on position.
b. Momentarily open throttle to allow solenoid plunger to extend, then adjust A/C idle speed to specifications with solenoid plunger screw.
c. Turn off A/C and reconnect wiring harness connector to compressor.
17. Remove enrichment tool and install PCV tube in air cleaner. Reconnect vacuum hoses to proper fittings.
Series 10-30/1500-3500 W/Heavy Duty Emissions
Light Duty vehicles with a Gross Vehicle Weight Rating above 8500 Lbs. Heavy Duty Emissions vehicles. A/C control must be in off position except where noted. Perform adjustments with transmissions in neutral on all models.
1. Remove air cleaner and plug related vacuum fittings. Disconnect and plug other vacuum hoses as directed by vehicle emission control label.
2. Remove limiter cap from each mixture screw, taking care not to damage screws. Mixture adjusting screws are preset and sealed. If it is necessary to adjust idle mixture, refer to ``Concealment Plug Removal'' in the appropriate carburetor section to remove plugs sealing screws.
3. Turn each mixture screw in (clockwise) until lightly seated, then back screws out 2 turns.
4. Connect tachometer and vacuum gauge to engine following manufacturer's instructions.
5. Start engine and run at fast idle until it reaches normal operating temperature.
6. Adjust curb idle speed to specifications with throttle stop screw on carburetor.
7. Adjust mixture screws one at a time. Turn each screw in (clockwise) until RPM begins to drop, then back screw out to obtain maximum RPM at the highest steady vacuum reading (best idle).
8. Repeat steps 6 and 7 to obtain best idle at specified curb idle speed.
9. If necessary, adjust curb idle speed to specifications.
10. Using RTV sealant, or equivalent, seal idle mixture needle setting to prevent tampering and loss of fuel vapors.
11. Adjust throttle lever actuator, if equipped, as follows:
a. With engine warm and choke in wide open position, set curb idle to specifications.
b. Using a suitable vacuum pump, apply sufficient vacuum to actuator to fully extend plunger.
c. Manually open throttle and allow to close against extended plunger, then with plunger held inward, turn plunger screw in or out to obtain specified RPM as directed on vehicle emission control label.
12. Check and, if necessary, adjust fast idle speed to specifications.
13. Reconnect all vacuum hoses and install air cleaner.
1983-87 Models W/E2ME & E4ME Carburetors (C3 System) Except 1985-86 California 10-30 1500-3500 Series
The C3 emissions system used on these engines, provide precise control of air/fuel mixture during all ranges of engine operation. Because of this system control, adjustment procedures must be followed in exact sequence to ensure correct mixture adjustment. Dwell readings from the Mixture Control (MC) solenoid are used for adjustment calibration. If unable to obtain specified readings, refer to the C3 System Section.
MC SOLENOID EXTERNAL GAUGE CHECK
MC solenoid travel must be within specifications before idle mixture can be adjusted. Perform check with engine off and air cleaner removed. Before proceeding, modify float gauge J-34935 or equivalent, to fit in ``D'' shaped vertical vent on carburetor air horn.
1. Insert gauge in ``D'' shaped hole. Press down on gauge and release, making sure that gauge moves freely, without binding.
2. With gauge released (solenoid up position), read gauge at eye level and record reading that lines up with top of air horn casting.
3. Press down lightly on gauge until bottomed. Record reading where gauge lines up with top of air horn casting.
4. Subtract reading in step 2 from reading in step 3 to obtain total MC solenoid travel.
5. If total MC solenoid travel is 4/32, proceed to ``Idle Air Bleed Valve Adjustment.'' If travel is not within specifications, MC solenoid must be adjusted.
Fig. 2 Mixture control solenoid adjustment:
Fig. 3 Lean & rich mixture screw plug locations:
Fig. 4 Lean & rich mixture screw plug installation:
MC SOLENOID ADJUSTMENT
1. Remove carburetor air horn and gasket, MC solenoid plunger and plastic filler block.
2. Remove throttle side metering rod.
3. Install MC solenoid gauging tool J-33815-1, BT-8253-A or equivalent over metering rod jet guide rod, Fig. 2, then reinstall MC solenoid plunger.
4. Hold MC solenoid plunger in down position and turn lean mixture screw counterclockwise until plunger just breaks contact with gauging tool. Use tool J-28696, BT-7928 or equivalent to adjust lean mixture screw.
5. Slowly turn lean mixture screw clockwise until plunger just contacts gauging tool. Adjustment is correct when plunger contacts both solenoid stop and gauging tool, in down position. If adjusted position is less than 3/4 turn different than original position, original adjustment was correct.
6. Remove solenoid plunger and gauging tool, then reinstall metering rod and plastic filler block.
7. Remove rich mixture screw from underside of air horn.
8. Remove lean and rich mixture screw sealing plugs from air horn, Fig. 3, using a suitable punch.
9. Reinstall rich mixture screw turning until lightly seated, then back screw out 1/4 turn and reinstall air horn using a new gasket.
10. Adjust MC solenoid travel to 4/32 inch with rich mixture screw, checking as outlined in ``MC Solenoid External Gauge Check.''
11. Install new plugs over lean and rich mixture screws as shown, Fig. 4, then proceed to ``Idle Air Bleed Valve Adjustment.'' New plugs must be installed, as directed, over lean and rich mixture screws in order to retain settings and to prevent fuel vapors from entering the atmosphere.