Fuel - Black Exhaust, Vacuum Break/Choke Pull-off Test
85cadillac02Bulletin No. T 85-97
File in Group 6C
Number 100
Corp. Ref. No. 8045908
Date July '85
SUBJECT: CARBURETOR VACUUM BREAK TESTING PROCEDURE
MODELS AFFECTED: ALL CARBURETOR EQUIPPED MODELS WITH VACUUM BREAKS
Hard starting or poor warm-up performance on a carbureted engine may be due to a leaking vacuum break unit. The vacuum break, sometimes called the "choke pull-off", opens the carburetor choke valve against the tension of the thermostatic choke coil during cold engine start-up. A vacuum break unit with a leaking diaphragm will not open the choke valve to the proper position, and may cause a cold engine to load up with fuel, resulting in black exhaust smoke.
VACUUM BREAK TESTING PROCEDURE:
FIGURE 1 - PLUGGING AIR BLEED HOLES:
1. Determine whether the vacuum break has a bleed orifice. If it does, it should be plugged as shown. See Figure 1 for possible locations.
^ Most rear or secondary side units have a bleed.
^ Most front or primary side units do not.
FIGURE 2 - Vacuum Break Testing:
2. Use hand-held vacuum pump to apply 15" Hg (51 kPa) vacuum to the vacuum break (Figure 2).
A. The vacuum break plunger should move full travel. Apply finger pressure to plunger to see that it has moved through full travel. If not, replace the vacuum break and adjust to specification. The labor operation time for replacing the vacuum break unit includes adjustment.
B. The vacuum break diaphragm should hold vacuum for at least twenty seconds. If it does not, replace the vacuum break and adjust to specification.
REMINDER: The carburetor vacuum break is covered under the Five-Year/50,000-Mile Emission Control Systems Warranty. Refer to the "Cadillac Service Policies and Procedures Manual."