Chevrolet Light Duty Truck 1973 Service Manual page 467

ROCHESTER CARBURETOR DIAGNOSIS
MODELS M , M V - 2 G , 2 G V - 4 M , 4 M V .
NOTE: These problems can be caused by many things other than carburetor. Check the following engine tune-up items
before proceeding w ith carburetor items.
Engine compression, spark plugs, ignition point gap and condition, ignition timing, fuel pump pressure and volume,
plugged fuel filters or fuel lines and intake manifold for vacumn ieaks. Make sure all emission control parts are installed and
operating properly. This includes all emission systems solenoids and hoses where used.
Problems o f roughness slight hesitation, surge or poor fuel economy should not be diagnosed before an allowable engine
break in period.
ALL MODELS M , M V - SINGLE BARREL
Problem:
E N G I N E C R A N K S ( T U R N S O V E R ) W I L L N O T S T A R T O R S T A R T S H A R D W H E N C O L D .
POSSIBLE CAUSE
Improper starting procedure used.
No fuel in gas tank
Choke valve not closing sufficiently when cold.
Choke valve or linkage binding or sticking.
No fuel in carburetor.
Engine Flooded.
NOTE: To check for flooding, remove the air cleaner,
with the engine off, and look into the carburetor bores.
Fuel w ill be dripping o ff nozzles and/or the carburetor
w ill be very wet.
Carburetor flooding
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1
Check w ith the customer to determine if proper starting
procedure is used, as outlined in the owner's manual.
Add fuel. Check fuel gauge for prosper operation.
Adjust the choke thermostatic coil. Use procedure H or I.
Realign the choke valve or linkage as necessary. If caused
by d irt and gum, clean w ith automatic choke cleaner.
Do not oil choke linkage.
adjustments using procedure D, E or F.
1. Remove fuel line at carburetor.
line and run into metal container.
tension coil wire from center tower on distributor cap
and ground. Crank over engine — if there is no fuel
discharge from the fuel line, check fo r kinked or bent
lines. Disconnect fuel line at tank and blow out w ith
air hose, reconnect line and check again for fuel dis­
charge. If none, replace fuel pump.
adequate flow, as outlined in service manual.
2. If fuel supply is o.k., check the following:
a. Inspect fuel filters. If plugged replace.
b. If filters are o.k., remove air horn and check fo r a
bind in the float mechanism or a sticking float
needle. If o.k., adjust float as specified. Use proce­
dure A.
Check to determine if customer is using proper carbu­
retor unloading procedure.
the floor and check the carburetor to determine if the
choke valve is opening.
age and unloader, as specified. Use procedure G.
NOTE: Before removing the carburetor air horn, use the
following procedure which may eliminate the flooding.
1. Remove the fuel line at the carburetor and plug. Crank
and run the engine until the fuel bowl runs dry. Turn
o ff the engine and connect fuel line. Then re-start and
run engine. This w ill usually flush d irt past the carbu­
retor float needle and seat.
2. If d irt is in fuel system, clean the system and replace
fuel filters as necessary.
move the carburetor unit. Disassemble and clean.
E N G IN E FUEL 6 M - 4 3
If parts are replaced, check
Connect hose to fuel
Remove the high
Check pump for
Depress the accelerator to
If not, adjust the th ro ttle link­
If excessive d irt is found, re­
LIGHT DUTY TRUCK SERVICE MANUAL