Automobile Maintenance Guidelines: Petrol Engine (Carburetor)

Petrol Engine(Carburetor) Faults

(1) Starter motor won't crank the engine

(2) Starter motor cranks the engine but it won't start.

(3) Engine starts but it won't run smoothly.(Engine misses)

(4) Engine overheats.

(5) Engine backfires.

(6) Knocking sound in the engine.

(7) Engine lacks power.

(8) Abnormal engine oil pressure.

(9) Excessive engine oil consumption.

(10) Excessive fuel consumption

(11) Excessive engine vibration.

(1) Starter motor won’t crank the engine.

Possible Causes :

1. Engine jammed.

2. Transmission not in neutral position.

3. Seat belts not fastened.

4. Battery discharged, terminals corroded or loose.

5. Damaged or disconnected battery cables.

6. Starter motor defective or pinion jammed in fly wheel.

7. Starter switch defective or wire connections improper.

(2) Starter motor cranks the engine but it won’t start.
Possible Causes :

1. Incorrect starting procedure.

2. Engine oil too thick for weather condition.

3. Air cleaner blocked.

4. Ignition system defects ;

(A) Weak battery or insufficient charging.

(B) Ignition timing incorrect.

(D) Defective or leaky plug wires.

(E) Spark plugs defective (Burnt, fouled or incorrectly adjusted plug gaps).

(F) Loose wire connections.

5. Fuel system defects ;

(A) Contaminated or improper grade of fuel.

(B) No fuel or air bubbles in the fuel line.

(D) Fuel filter blocked.

(E) Fuel pump defective.

(F) Air leaking into the carburetor.

(G) Carburetor over-choked or flooded.

(H) Carburetor fouled, defective or incorrectly adjusted.

6. Insufficient cylinder compression :

(A) Piston rings, cylinders worn out.

(B) Compression leaks between cylinder head and block due to damaged or improperly tightened gasket.

(C) Improper valves or valve operation :

(a) Valve timing incorrect.

(b) Insufficient valve clearance.

(3) Engine starts but it won’t run smoothly (Engine misses)

Possible Causes :

1. Air cleaner blocked.

2. Restricted exhaust.

3. Ignition system defects :

(A) Weak battery or low charging rate.

(B) Defective Ignition coil, distributor or condenser.

(D) Spark plugs defective (Burnt, fouled or incorrectly adjusted plug gaps)

(E) Loose wire connections.

4. Fuel system defects :

(A) Fuel contaminated or of lower grade.

(B) Fuel pipes or fuel filters blocked.

(D) Fuel tank breather blocked.

(F) Fuel pump fouled or defective.

(G) Carburetor throttle valve partially opening.

(H) Air leaking into the inlet manifold or carburetor.

(I) Incorrect carburetor adjustments (Lean air/fuel mixture).

5. Insufficient cylinder compression :

(A) Piston rings, cylinders worn out.

(B) Compression leaks between cylinder head and block due to damaged or improperly tightened gasket.
(C) Improper valves or valve operation :

(a) Valve timing incorrect.

(b) Insufficient valve clearance.

(4) Engine overheats.

Possible Causes :

1. Cooling system defects :

(A) Insufficient or no coolant.

(B) Leakage of coolant to outside through radiator, radiator pressure cap, expansion tank, radiator hose, hose connections, water pump seals, drain plug etc.

(D) Fan belt loose or slipping with oil.

(E) Fan blades warped causing poor air flow.

(F) Fan drive clutch defective.

(G) Fan drive motor defective or no electricity supply.

(H) Cooling and coolant flow restricted due to corrosion.

(I) Thermostat stuck or improperly installed.

(J) Defective water pump which does not circulate enough water.

2. Temperature gauge or indicator defective.

3. Exhaust system obstructed (high exhaust back pressure.)

4. Improperly operating emission controls.

5. Ignition retarded (Vacuum advance not operating).

6. Carburetor incorrectly adjusted (Lean air/fuel mixture).

7. Valve timing late (Slack timing chain).

8. Insufficient engine oil level.

9. Cylinder head gasket leaking.

10. Piston rings or bearings too tight causing excessive engine friction.

11. Brakes dragging or clutch slipping.

12. Overloading of the engine.

13. Continuous driving in low gears.

14. Hot climate conditions, high altitude operation.

(5) Engine backfires

Possible Causes :

1. Intake backfiring :

(A) Ignition timing advanced.

(B) Cross-firing spark plug cables (Damaged or leaking cable insulation)

(D) Spark plugs of wrong heat range (Hot plugs)

(E) Hot valves or carbon deposits.

(F) Carburetor defects (Lean air/fuel mixture)

(G) Defective anti-backfire valve.

(H) Engine overheating.

2. Exhaust backfiring :

(A) Exhaust valve clearance insufficient.

(B) Carburetor defects :

(a) Rich air/fuel mixture.
(b) Carburetor flooding.
(c) Incorrect carburetor throttle valve adjustment.

(6) Knocking sound in the engine.

Possible Causes :

1. Combustion knocks (Detonation) :

(A) Ignition timing advanced (Ignition advance retard mechanism defective)

(B) Spark plugs of wrong heat range.

(D) Incorrect grade of fuel (Low octane).

(E) Excessive carbon deposits in cylinders.

(F) Cylinder head facing too much.

(G) Waste gate inoperative (Turbo Engines)

(H) In low gear when climbing a hill.

2. Mechanical knocks :

(A) Valve clearance excessive.

(B) Broken, worn or seized piston rings.

(D) Excessive crankshaft end-play.

(E) Damaged main or connecting rod bearing.

(F) Flywheel, pressure plate loose.

(7) Engine lacks power.

Possible Causes :

1. Ignition system defects :

(A) Weak battery or low charging rate.

(B) Defective Ignition coil, distributor or condenser.

(D) Spark plugs defective (Burnt, fouled or incorrectly adjusted plug gaps)

(E) Loose wire connections.

2. Fuel system defects :

(A) Fuel contaminated or of lower grade.

(B) Fuel pipes or fuel filters blocked.

(D) Fuel tank breather blocked.

(F) Fuel pump fouled or defective.

(G) Carburetor throttle valve partially opening.

(H) Air leaking into the inlet manifold or carburetor.

(I) Incorrect carburetor adjustments (Lean air/fuel mixture).

3. Insufficient cylinder compression :

(A) Piston rings, cylinders worn out.

(B) Compression leaks between cylinder head and block due to damaged or improperly tightened gasket.

© Improper valves or valve operation :

(a) Valve timing incorrect.

(b) Insufficient valve clearance.

(d) Valves stuck open due to bent push rod or broken spring.

4. Fouled air cleaner.

5. Exhaust pipe or silencer blocked.

6. Engine over heated.

7. Excessive carbon deposits in cylinders.

8. Clutch slipping or brakes dragging.

9. Defective torque converter or auto gear box.

10. Use of thick engine oil.

11. Excessive rolling resistance due to,

(a) Wheel alignments improper.

(b) Brakes dragging.

(8) Abnormal engine oil pressure.

Possible Causes :

1. Low engine oil pressure :

(A) Engine oil level insufficient or no oil.

(B) Excessively thin or hot engine oil.

(D) Oil filter contaminated.

(E) Oil pressure indicator defective.

(F) Oil pressure gauge pipe line clogged.

(G) Oil circulation obstructed through pipes, oil gallery, oil pump or oil filter.

(H) Oil leaks through broken or cracked pipe lines, pipe connections, oil gallery or oil seals.

(I) Oil pressure relief valve leaky (Weak springs)

(J) Excessive bearing clearances.

(K) Damaged main or connecting rod bearings.

(L) Wrong grade of oil for weather condition.

(M) Oil pump is worn out

2. High engine oil pressure :

(A) Oil pressure relief valve stuck.

(B) Excessively strong relief valve spring.

(D) Excessively thick engine oil.

(9) Excessive engine oil consumption.

Possible Causes :

1. Engine oil level too high

2. Engine oil leaking

3. Cylinders or piston sleeves worn out

4. Piston oil rings worn or stuck to the ring grove

5. Valve guide oil seals worn out

6. Cylinder head gasket improperly tightened or damaged

(10) Excessive fuel consumption.

Possible Causes :

1. High speed driving.

2. Continuous driving in low gears.

3. Clogged air cleaner.

4. Fuel leaks (Through fuel tank, fuel line, fuel pump or carburetor)

5. Carburetor defective or incorrectly adjusted (Jets worn, choke valve partially open)

6. Engine misfire (Poor ignition)

7. Auto transmission slipping (Auto Gear)

8. Clutch slipping or brakes dragging

9. Excessive rolling resistance due to,

(A) Wheel misalignment.

(B) Under inflated tires.

10. Insufficient cylinder compression :

(A) Piston rings, cylinders worn out.

(B) Compression leaks between cylinder head and block due to damaged or improperly tightened gasket.

(a) Valve timing incorrect.

(b) Insufficient valve clearance.

(11) Excessive engine vibration.

Possible Causes :

1. Defective vibration damper.

2. Unbalanced or loose fly wheel.

3. Excessive crankshaft end play.

4. Loose or broken engine mounts.

5. Engine idle speed too low.

6. Engine miss.