Carburettor Problems (Automobile)

9.20.

Carburettor Problems

Carburettor problems are usually encountered as a flooding condition, malfunctioning choke, severe backfiring, sticking throttle, inability to set idle, engine hunting, popping back, or no action of acceleration pump. Excessive carbon monoxide in the exhaust indicates a carburettor problem. Lean carburettor mixtures create surge-type or roughness-type driveability problems on emission-controlled engines. Some of the problems are high lighted as follows.

Flooding.

Flooding in the carburettor occurs due to excessive flow of petrol from the main jet. This may be caused due to (i) too much petrol pressure in the float chamber on account of the fuel pump, (ii) the level of jet being lower than that of the float chamber, because of improper fitting, causing natural flow, and (Hi) damaged float providing a high level of petrol in the float chamber.

Engine Hunting.

This problem is indicated when engine runs in a series of surges and speed of the engine fluctuates intermittently. Adjustment of the slow running air screw rectifies the problem.

Popping Back.

This problem occurs due to explosions in the carburettor with characteristic spitting or roughing sound due to a weak mixture, retarded ignition, improper seating of inlet valves, or weak or broken valve springs. Cold engines are more susceptible to this problem due to incomplete combustion.


Back Firing.

If partially burnt or un-burnt gas goes into the exhaust manifold, it burns in the silencer when it comes into contact with atmospheric air. This may occur due to too weak a slow running mixture or a faulty exhaust valve.

Following are the problems caused by faulty internal conditions of the carburettor:
(i) Excessive Fuel Consumption This can result from
(a) Defective float or high float level,
(b) A dirty or sticking float valve,
(c) Worn jets,
(d) A stuck metering rod or power piston,
(e) A stuck accelerator-pump check valve, (/) A leaky carburettor,
(g) Idle too rich or too fast, and
(h) A dirty air filter.
(ii) Lack of Engine Power for Acceleration or High-speed Performance
This can result from
(a) A stuck power piston or valve.
(6) A dirty air filter,
(c) Choke not operating or stuck,
id) Throttle valve not fully opening,
(e) Rich mixture, due to excessive fuel consumption,
(/) Air leakage into the manifold,
(g) A low float level, and
(h) Clogging of the fuel jets due to dirt or gum, or metering rod not clearing the jets.
(Hi) Poor Idle
This can result from
(a) A leaky vacuum hose,
(b) Stuck PCV valve,
(c) Retarded timing,
(d) A clogged idle system, and
(e) Improper adjustment of idle mixture or speed.
(iv) A Smoky and Black Exhaust
This is due to an over-rich mixture, which is mainly the result of excessive fuel consumption.

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