13 Motore3. Adjustments
USE AND MAINTENANCE MANUAL CHAPTER 3
ADJUSTMENTS2-Strokes - Edition 01 / 2023
100
Examples of carburetor setting depending on symptom
(*) : In case of hard breathing, check the carburetor breather hoses for clogging.This should be taken simply for an
example. It is necessary to set the carburetor while checking the operating conditions of the engine and discoloration
of spark plugs. Normally, carburetor setting is made by means of the main jet, jet needle clip position, pilot jet and pilot
air screw.
Sintomo Impostazione Controllo
At full throttle:
– Stall at high speeds
– (*) Hard breathing
– Shearing noise
– Whitish spark plug
• Lean mixture
Increase main jet calibration no.
(Gradually)
Discoloration of spark plug:
• If tan color, it is in good condition.
If cannot be corrected:
– Clogged float valve seat
– Clogged fuel hose
– Clogged fuel cock
At full throttle:
– Speed pick-up stops
– Slow speed pick-up
– Slow response
– Sooty spark plug
• Rich mixture
Decrease main jet calibration no.
(Gradually)
(*) In case of racing slight enrichment of
mixture reduces engine trouble.
Discoloration of spark plug:
• If tan color, it is in good condition.
If cannot be corrected:
– Clogged air filter
– Fuel overflow from carburetor
– Clogged air intake or clogged air filter.
Lean mixture
Lower jet needle clip position.
(1 groove down)
The clip position is the jet needle groove
on which the clip is installed. The positions
are numbered from the top.
If a change in the clip position (1 groove)
is effective, try another jet needle that
provides a difference of 0.5 in the clip
position.
Rich mixture
Raise jet needle clip position.
(1 groove up)
1/4–3/4 throttle:
– (*) Hard breathing
– Lack of speed
Lower jet needle clip position.
(1 groove down)
1/4–1/2 throttle:
– Slow speed pick-up
– White smoke
– Poor acceleration
Raise jet needle clip position.
(1 groove up)
Closed to 1/4 throttle:
– (*) Hard breathing
– Speed down
Use jet needle having a smaller diameter.
Closed to 1/4 throttle:
– Poor acceleration
– White smoke
Use jet needle with a larger diameter.
Unstable at low speeds:
– Pinking noise
Lower jet needle clip position.
(1 groove down)
Turn in pilot air screw.
Poor response at extremely low
speed
Reduce pilot jet calibration No.
Turn out pilot air screw.
If not effect, reverse the above
procedures.
– Dragging brake
– Overflow from carburetor
Poor response in the low to
intermediate speeds
Raise jet needle clip position.
If not effect, reverse the above
procedures.
Scarsa risposta quando si apre
rapidamente l’acceleratore
Check overall settings.
Use main jet having lower calibration No.
Raise jet needle clip position.
(1 groove up)
If not effect, reverse the above
procedures.
Check air filter for fouling.
Poor engine operation
Turn in pilot air screw. Check throttle valve operation.
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