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RE-ASSEMBLING
& HOW TO TRACE FAULTS
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RE-ASSEMBLING
RE-ASSEMBLING
after dismantling. See that the washer on the bottom of
the jet block is in good condition, otherwise fuel will
leak across its face causing rich erratic running. if the
washer is faulty it should be replaced by a new one. When
replacing the throttle see that the jet needle goes into
the centre hole in the jet block and once in, check the
throttle works freely when the mixing chamber cap (2) is
screwed down firmly by spring clip (18).
When
re-assembling the float see that the narrow leg portion
of its hinge is uppermost, as this operates the float needle.
Care should be taken to see that the joint faces of the
side cover and body are not damaged or warped and that the
joint washer is in good condition, otherwise difficulty
will be experienced in making a petrol tight joint.
HOW
TO TRACE FAULTS
| 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 the banjo gauze is clear and allows ample flow.
Verify there is no flooding. |
| 2.
Looking for air leaks. |
At
the connection to the engine.
Or due to leaky inlet valve stems.
|
| 3.
Defective or worn parts. |
Slack
throttle or worn needle jet.
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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If the jet block 16 is not tightened
up by washer and nut 14, richness will be caused
through leakage of petrol. |
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Air cleaner choked up. |
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Needle jet worn large. |
Sparking
plug sooty.
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Spitting
in carburetter.
Erratic slow running.
Overheating
Acceleration poor.
Engine goes better if;
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throttle not wide open or air
valve is partially closed |
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Has air cleaner been removed |
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Jets partially choked up |
REMOVING
the silencer or running with a racing silencer requires
a richer setting and a larger main jet.
|
NOTE:
Verify
correctness of fuel feed, stop air leaks, check over ignition
and valve operation and timing. Now at throttle position
shown on sheet
7, fig 5, test to see if the mixture is rich or weak.
This is done by partially closing the air valve, and if
the engine runs better weakness is indicated, but if the
engine runs worse richness is indicated.
| TO
CURE RICHNESS |
TO
CURE WEAKNESS |
- Fit
smaller main jet.
- Screw
out pilot air screw.
- Fit
a throttle with larger cut-away
- Lower
needle one or two grooves
|
- Fit
larger main jet
- Screw
pilot air screw in.
- Fit
a throttle with smaller cut-away.
- Raise
needle one or two grooves.
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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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