GMC 1976 ZEO 6083 Maintenance Manual page 350

6M- 8 ENGINE FUEL SYSTEM
ENGINE STARTS AND STALLS
Possible Cause
Corrective Action
Engine flooded.
1 . Check to determine if customer is using proper
NOTE : To check for flooding, carburetor unloading procedure. Depress the
remove air cleaner with engine accelerator to the floor and check carburetor to
off, and look into carburetor determine if the choke valve is opening. If not,
bores. Fuel will be dripping off
adjust throttle linkage and unloader .
discharge nozzles and carburetor
bores will be very wet.
2 . If choke unloader is working properly - check
for carburetor flooding .
NOTE : Before removing the carburetor air horn, use
the following procedure which may eliminate the
flooding .
Remove the fuel line at carburetor and plug . Start
and run the engine until the fuel bowl runs dry.
Turn off engine and connect fuel line . Then restart
and run engine . This will usually flush dirt past
the carburetor float needle and seat .
3 . If dirt is in the fuel system, clean the system
and replace fuel filter as necessary. If excessive
dirt is found, remove the carburetor unit .
Disassemble and clean.
4. Check float needle and seat for proper seal .
If a needle and seat tester is not available,
apply mouth suction needle seat with needle
installed. If needle and seat is defective, replace
with factory matched set.
5 . Check for fuel leaks into float, bent float
arm or binds in the float hanger . Free up or
replace parts as necessary .
NOTE : A solid float can be checked for fuel absorp-
tion by lightly squeezing between fingers. If wet-
ness appears on surface or float feels heavy
(check with known good float), replace float
assembly .
6. After making preceding checks, adjust float
assembly .
Possible Cause
Corrective Action
Engine does not have enough fast
Check and reset fast idle screw and fast idle cam.
idle speed when cold .
Choke vacuum break unit is not
1 . Adjust choke vacuum break assembly to specifi-
adjusted to specification or is
cations.
defective.
2. If adjusted O.K ., check the vacuum break unit for
proper operation as follows.
Connect a piece of hose to the nipple on the vacuum
break unit and apply suction by mouth or vacuum
source . Diaphragm plunger should move inward and
hold vacuum . If not, replace diaphragm unit .
NOTE : Always check fast idle cam (choke rod)
adjustment first before adjusting vacuum break
unit .