Bronco L6-300 4.9L VIN Y 1-bbl (1983)
Air/Fuel Mixture: Adjustments
Fig. 3 Propane enrichment specifications chart
The idle mixture screw is protected by a cap which prevents tampering during normal tune up procedures. If it is evident that idle mixture requires
adjustment, remove the cap as outlined in ``Tamper-Resistant Cap Removal'' procedure in the appropriate carburetor section. Refer to ``Propane
Enrichment Chart,'' Fig. 3, for specifications.
1983, 84, 86
1.
Apply parking brake and block wheels, then disconnect automatic brake release, if equipped, and plug vacuum hose.
2.
Connect suitable tachometer.
3.
Disconnect flexible air hose from air cleaner duct. Insert hose of propane enrichment tool T75L-9600-A or equivalent, 3/4 of way into air cleaner
duct. Use tape to secure hose if necessary.
4.
On 1983 models with YFA-1V feedback carburetor, disconnect two vacuum lines from second and third switches of four switch panel and plug
vacuum lines.
5.
On all models, check that ignition timing is set correctly. All vacuum signal lines should remain connected to air cleaner assembly when relocating
assembly to make carburetor adjustments. Air cleaner must be in place when measuring engine speeds. Prolonged idling can cause catalyst
overheating and excessive underbody temperatures.
6.
On 1983 models, check engine curb idle speed and adjust, if necessary. On 1984 - 86 models, set A/C-heat selector off and check that all
accessories are off.
7.
On all models, remove PCV valve from grommet. On 1984 - 86 models, locate and disconnect crankcase closure hose at air cleaner end.
8.
On 1984 - 86 models, check that idle speed control motor is connected electrically.
9.
On all models, run engine at 2500 RPM in Neutral for 15 seconds before each mixture check. If mixture check is not completed within 60 seconds,
repeat clean out step.
10.
On 1984 - 86 models, return engine to idle and disconnect idle speed control motor wiring.
11.
On all models, place transmission in Neutral with engine idling and at normal operating temperature. Gradually open propane tool valve and
observe engine speed gain on tachometer. When engine speed reaches maximum and then begins to drop off, note amount of speed gain. If engine
speed does not drop off, check propane cartridge gas supply. If necessary repeat steps 8 through 11 with new propane cartridge.
12.
Compare measured speed gain to specified speed gain. If measured speed gain is correct proceed to step 16. If carburetor is equipped with
tamper-resistant idle adjustment feature, carburetor must be removed from vehicle. Refer to Carburetor Section to remove plugs. If idle fuel
mixture adjustment is necessary, adjust mixture according to reset RPM specifications.
13.
If measured speed gain is higher than speed gain specification, turn mixture screw counterclockwise (rich) and repeat steps 8 through 11 until
measured speed rise meets reset RPM specification. After final adjustment, proceed to step 15.
