How to trace faults
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carburettor with pilot jet system |
How It Works & Part Names |
General Hints & Tips |
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How to trace faults |
Parts to tune up with |
How to tune up |
| There are only TWO possible faults in carburation; either RICHNESS of mixture or WEAKNESS of mixture, so in case of trouble, decide which is the cause, by; | |
| 1. Examining the petrol feed. | Verify
jets and passages are clear. Verify ample flow. Verify there is no flooding. |
| 2. Looking for air leaks. |
At
the connection to the engine. |
| 3. Defective or worn parts. | Slack
throttle or worn needle jet. The mixing chamber union nut not tightened up, or loose jets. |
| 4. TEST WITH THE AIR VALVE, | to see if by richening the mixture, the results are better or worse. |
INDICATIONS OF:
| RICHNESS | WEAKNESS | ||||||||||||
| Black
smoke in exhaust. Petrol spraying out of the carb. Four strokes, eight stroking. Heavy, lumpy running. Heavy petrol consumption.
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Spitting
in carburetter. Erratic slow running. Overheating Acceleration poor. Engine goes better if;
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NOTE:
Verify correctness of fuel feed, stop air leaks, check over ignition and valve operation and timing. DECIDE BY TEST WHETHER RICHNESS OR WEAKNESS IS THE TROUBLE AND AT WHAT THROTTLE POSITION. See throttle opening diagrams, sheet 7 .
PROCEDURE:
If at a particular throttle opening you partially close the air valve and the engine goes better, weakness is indicated. If the running is worse, richness is indicated. THEN YOU PROCEED TO ADJUST THE APPROPRIATE PART AS INDICATED AT THE BOTTOM OF SHEET 7 FOR THAT THROTTLE POSITION.
FAULT AT THROTTLE POSITIONS (Indicated on sheet 7)
NOTE: It is not correct to cure a rich mixture at half throttle by fitting a smaller main jet because the main jet may be correct for power at full throttle, the correct way is to lower the needle.
CHANGING FROM STANDARD PETROLS TO SPECIAL FUELS, such as alcohol mixtures will, with the same setting in the carburetter, certainly cause weakness of mixture and possible damage from overheating.
Verify correctness of fuel feed, stop air leaks, check over ignition and valve operation and timing. DECIDE BY TEST WHETHER RICHNESS OR WEAKNESS IS THE TROUBLE AND AT WHAT THROTTLE POSITION. See throttle opening diagrams, sheet 7 .
PROCEDURE:
If at a particular throttle opening you partially close the air valve and the engine goes better, weakness is indicated. If the running is worse, richness is indicated. THEN YOU PROCEED TO ADJUST THE APPROPRIATE PART AS INDICATED AT THE BOTTOM OF SHEET 7 FOR THAT THROTTLE POSITION.
FAULT AT THROTTLE POSITIONS (Indicated on sheet 7)
| TO CURE RICHNESS | TO CURE WEAKNESS |
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NOTE: It is not correct to cure a rich mixture at half throttle by fitting a smaller main jet because the main jet may be correct for power at full throttle, the correct way is to lower the needle.
CHANGING FROM STANDARD PETROLS TO SPECIAL FUELS, such as alcohol mixtures will, with the same setting in the carburetter, certainly cause weakness of mixture and possible damage from overheating.
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