ROUGH IDLE
Check engine vacuum using a vacuum gauge. Gauge should read approximately 18
inches at idle. If vacuum is low; check condition and location of all vacuum
hoses. Check carburetor base gasket and manifold gasket. Run an engine
compression test. Worn engine parts such as valves, rings, or camshaft will
cause a rough idle. Look at the ignition system (plugs, wires, cap and rotor).
Inspect the emission system. Pay particular attention to the charcoal canister,
the purge valve and the EGR valve. The EGR valve should be closed at idle.
BACKFIRING
It is nearly impossible for a carburetor to cause a vehicle to backfire. Make
sure that the spark plug wires are properly attached and that the distributor
cap is free of any carbon tracking. Check the ignition rotor to make sure that
it is In good condition, Set the ignition timing to manufacturers
specifications. Check the manifold vacuum with a vacuum gauge. A bad vacuum
leak can lean out the mixture enough to cause an engine backfire. Check the
engine compression. A leaking, burned, cracked, or stuck valve could be the
cause. A worn camshaft lobe or bad timing chain could also be at fault. Check
the choke operation. If the choke comes open too quickly the engine will be
lean when cold and backfire.
FLOODING
THERE ARE THREE COMMON REASONS FOR FLOODING
A. The engine is started and fuel flows over the top of the carburetor, or
pours into the intake manifold. This condition is generally a result of either
dirt between the needle and seat, or a stuck float. A light tap on the fuel
inlet fitting will sometimes cure this condition.
B. The engine is shut off and the fuel drips down the barrel(s) of the
carburetor. This condition can be caused by the fuel line being located too
close to a heat source such as a radiator hose or exhaust manifold. This causes
the fuel in the line to expand and be forced past the needle and seat causing
flooding. Also, fuel can boil inside the carburetor as the result of improper
or missing gaskets or spacers between the carburetor and the intake manifold. A
heat riser that is stuck In the closed position will cause excessive heat under
the carburetor and boil the fuel causing flooding and hard starting when the
engine is hot.
C. When there is excessive fuel pressure. Excessive fuel pump pressure can be
caused by a detective or worn out fuel pump. This condition will cause
flooding. Refer to manufacturers specifications for correct fuel pressures.
HESITATION
Check for proper EGR operation. The EGR valve should be closed at idle and when
the engine is cold. A malfunctioning EGR valve can cause HESITATION. Also,
check the ignition system and the timing. Make sure that the distributor
advance mechanism is functioning properly Other problem areas include cracked
or improperly connected vacuum lines or a clogged exhaust system. Excessive
alcohol content or additives in the fuel can lean out mixtures enough to cause
a HESITATION or engine surge.
HARD STARTING
A. WHEN THE ENGINE IS COLD, Check for proper choke operation When the engine is
cold prior to starting, press the accelerator down to floor and release. This
should cause the choke plate to close. When the engine starts, the choke should
open partially and continue to open as the engine warms up... When the engine
is warm, (lull operating temperature) the choke should be fully open. Doesn't
work this way?
B. WHEN THE ENGINE IS HOT, Excessive heat around the fuel system is indicated.
(See "FLOODING" above).
ENGINE WON'T IDLE DOWN
Check for mis-adjusted fast idle cam screw, curb idle screw, or dashpot. Check for proper operation and adjustment of all solenoids on the carburetor. Check choke circuit operation and make sure the base gasket is properly installed.
STUMBLES WHEN COLD
Check the heat riser valve in the exhaust manifold. It should be closed when cold. Also be sure that the choke heat tube that is in the manifold is not allowing exhaust gases to enter the choke housing. This will cause the choke to open prematurely Make sure that the choke pull-off operates properly Check for proper EGR operation (refer to hesitation section). Restricted or clogged crossover passage in the intake manifold will affect the choke operation.
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