Carburetor Service Diagnosis


The chart applies only to carburetors which meet specifications shown on page F 11.
Malfunction Possible CauseRemedy
1. Engine does not start despite properly functioning ignition and adequate fuel in tank. a) No fuel in fuel system. a) Clean main jets. Check fuel supply lines. Detach fuel line connecting pump with carburetor, actuate starter (ignition off). If fuel flows from pump, float needle valve is plugged; if no fuel flows from pump, possibly pump check valves are stuck or pump mechanism defective.
b) Carburetor floods. b) Check and clean float needle valve, check gasket at float needle valve assembly. Check float, replace if defective.
2. Uneven idling. a) Improperly adjusted idling. a) Readjust idling.
b) Idle jets or idle air bleed plugged. b) Clean idle jets or idle air bleed, as required.
c) Leak in the intake ducts. c) Check intake ducts, flange connections, and gaskets.
d) Defective idle mixture screws. d) Install new idle mixture adjusting screws.
3. Poor power transition (flat spot). a) Idle adjustment too lean. a) Readjust idling (check jets).
b) Improperly set float level. b) Readjust float level.
c) Improper injection quantity. c) Readjust injection quantity.
d) Intake ducts leaking. d) Check intake ducts, flange connections, and gaskets.
4. Engine stalls when throttle is quickly closed. Improper idle adjustment. Readjust idling.
5. Engine runs unevenly, misses, backfires. a) Mixture too rich. a) Check fuel pump pressure. Check float level. Check float needle valve.
b) Mixture too lean. b) Clean main jets. Check fuel lines. Check float level.
c) Intake duct leaking. c) Check intake ducts, flange connections, and gaskets.
6. High fuel consumption. a) High fuel pump pressure overriding float needle valve. a) Check fuel pressure.
b) Defective float (leaking). b) install new float.
c) Float needle valve not closing. c) Check float needle valve.
Last modified: Wed, 12 Jan 2005


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