250+ TOP MCQs on Petrol Engine Fuel Supply System – Carburettor Service and Adjustment and Answers

Automotive Engine Auxiliary Systems Quiz on “Petrol Engine Fuel Supply System – Carburettor Service and Adjustment”.

1. Using which among the following are the jets present in a carburetor should be cleaned?
a) Water and antifreeze
b) Diesel and petrol
c) Petrol and blast of air
d) Kerosene and wire
Answer: c
Clarification: The carburetor jets should first be cleaned with petrol and then with a blast of air and it should be never cleaned with wire because the screw adjustment helps in the smooth run of the engine at the required speed.

2. Concerning the idle port area which among the following decreases by screwing the idle screw?
a) Pressure
b) Clearance
c) Engine speed
d) Air – fuel
Answer: c
Clarification: Screwing the idle screw in the same direction decreases the idle port area and hence decreases the engine speed. Generally, this is done by screwing -in completely and then opening back by one or two turns.

3. What can we recognize if the color of the exhaust smoke is black?
a) Overheating of the engine
b) Loss of power
c) Unburnt carbon particle
d) Stalling of the engine
Answer: b
Clarification: The extra rich mixture when burnt has the colour of the exhaust in black which is caused due to unburnt carbon particles in the exhaust. Whereas the stalling of the engine, unburnt carbon particle and overheating of the engine happens for an extra weak mixture.

4. Which among the following is not an indication of the extra weak mixture?
a) Loss of power
b) Overheating of engine
c) Stalling of the engine
d) Surging while idling
Answer: d
Clarification: The extra weak mixture is recognized by flat spot while accelerating, stalling of the engine, loud popping in the carburetor, overheating of the engine and loss of the power. Whereas the surging while idling is due to extra rich mixture.

5. What is the main reason for throttle adjustment?
a) To know the play of the acceleration pedal
b) To decrease the engine speed
c) To check the float
d) Both decrease the engine speed andcheck the float
Answer: a
Clarification: The accelerator pedal throttle valve should be completely closed, while on pressing pedal fully, it should be in the full open position. This should be checked and in case of some action, the linkage must be adjusted, as provided for in the manufacturer’s manual.

6. What is the first step in removing the carburetor?
a) Remove the throttle and choke linkage
b) Adjustment of the carburetor screw
c) Wash with petrol
d) Clean with the blast of air
Answer: a
Clarification: To remove the carburetor, first of all, remove the air cleaner and disconnect the throttle and choke linkages. Next disconnect the vacuum advance unit and any other connection that many be there.

7. What is the number of rotation that has to be given to the idle screw to adjust the carburetor?
a) 2
b) 2.5
c) 1
d) 3
Answer: b
Clarification: The carburetor is screwed in completely and then opening back by two and a half turns. This screwing in the same decreases the idle port area and hence decreases the engine speed. The screw is adjusted until the engine runs smoothly at the required speed.

8. How many numbers of jets are present in a simple carburetor?
a) 1
b) 2
c) 3
d) 4
Answer: b
Clarification: There are 2 jets present in a simple carburetor they are the main jet and the pilot jet. These jets are very important and should never be cleaned with wire whereas they should be cleaned with petrol and then with a blast of air.

9. In which among the following does not depend on the carburetor to provide the correct mixture of air-fuel?
a) Idling
b) Crushing
c) Accelerating
d) Pressure relief
Answer: d
Clarification: The carburetor is a device that provides air-fuel mixture to the engine in all the working operation of an engine like the idling, crushing and accelerating period but whereas the pressure relief system has no connection to the carburetor.

10. Which among the following should never be used in the cleaning of jets present in a carburetor?
a) Petrol
b) Blast of air
c) Wire
d) Carb cleaner
Answer: c
Clarification: The jets present in a carburetor should never be cleaned with the wire as the wire damages the jets which may lead to an increase in the hole diameter. Whereas they can be cleaned with petrol followed by a blast of air and curb cleaner helps in cleaning any stubborn carbon particles present.

11. What can we say about the air-fuel mixture if the engine is stalling by itself?
a) The extra weak mixture is supplied
b) An extra rich mixture is supplied
c) Combustion in muffler
d) The color of the exhaust smoke is black
Answer: a
Clarification: When the engine is supplied with the extra weak mixture the stalling of the engine by itself is the indication when the extra weak mixture is supplied. Whereas combustion in the muffler and black exhaust smoke represents an extra rich mixture.

12. Which among the following is not an indication of a rich mixture?
a) Loud murder explosion
b) High fuel consumption
c) Surging while idling
d) Stalling of the engine
Answer: d
Clarification: The extra rich mixture can be recognized by Hugh fuel consumption, surging while idling, loud muffler explosion and black smoke from the exhaust. Whereas the stalling of the engine takes place only for an extra weak mixture.

13. Which among the following is not a secondary adjustment?
a) Accelerating pump
b) Metering rod
c) Floats
D) Idle adjuster
Answer: d
Clarification: Apart from the idle adjuster and throttle adjustment the other adjustments which are provided are accelerating pump, metering rod, floats,etc which must be performed as laid down in the user manual.

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