13 MAN-071
5- CARBURETTOR ADJUSTMENT GUIDE
1 T.O.
*
RICH LEAN
1 ¼ T.O. ¾ T.O.
1 ½ T.O.
*
T.O. = TURNS OPEN
Normally the correct setting of the mixture screws is the following:
L (close the screw completely and then open): 1.00 T.O. for HL 334B and 1.00 T.O. for HL 394A.
H (adjust T.O from closed to approximately): ¾ T.O. for HL 334B and 1.00 T.O. for HL 394A.
Based on various factors as altitude, ambient temperature etc. it might be necessary to adjust the carburetor to
optimize the performance of the engine.
ATTENTION:
- Never lean too much as lean mixture will overheat engine and cause seizure.
-
Do not force H or L closed. It may damage the precision machined orifice and make the carb
unserviceable.
-
The screws adjustment must be performed with warm engine.
(H)
Adjust T.O. from closed to
approximately: ¾ T.O. for
HL 334B and 1.00 T.O. for
HL 394A
(L)
Adjust T.O. from closed to approximately
1 T.O
(I)
Close by further 1 ½ T.O
after contact with throttle
lever.
Start the engine and warm it. If R.P.M. too
high adjust I counterclockwise until clutch is
disengaged.
Turn c.c.w. until max. R.P.M.
is reached. Adjust further
fractionally for rich idle.
Trigger accelerator.
(L)
Slowly adjust clockwise
Continue to turn clockwise
until max. R.P.M. is reached.
Adjust c.c.w. fractionally for
rich idle.
Trigger accelerator.
Engine is now idling at max. attainable
R.P.M. or slightly lower on rich side
Adjust I counterclockwise until 2000 ÷ 2500
R.P.M. is reached
Recheck L screw for optimum setting
required
Adjust H until best possible free speed is
reached. Turn clockwise for higher R.P.M.
Counterclockwise for lower R.P.M.
Adjust L slightly richer by
1/8 ÷ ¼ T.O.
Return to idle and check acceleration for
quick response and smooth pick-up.
Engine is ready to operate
( I )
THROTTLE
SPEED SCREW
( L ) LOW SPEED FUEL MIXTURE
( H ) HIGH SPEED FUEL MIXTURE
MIXTURE sscrew
MMMIXTURESCREW
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