| 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.
Or due to leaky inlet valve stems.
|
| 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.
|
-
|
If the jet block F is not tightened
up by washer and nut E, richness will be caused
through leakage of petrol. |
|
-
|
Air cleaner choked up. |
|
-
|
Needle jet worn large. |
Sparking
plug sooty.
|
Spitting
in carburetter.
Erratic slow running.
Overheating
Acceleration poor.
Engine goes better if;
|
-
|
throttle not wide open or air
valve is partially closed |
|
-
|
Has air cleaner been removed |
|
-
|
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. 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 |
- 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.
|
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.
|
