Yamaha RS90NL, Дополнительное руководство по обслуживанию

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12
INSP
ADJ
CARBURETOR TUNING
Troubleshooting
Main jet selection chart
Spark plug color Diagnosis Remedy
Light tan or gray Carburetors are tuned prop-
erly.
Dry black or fluffy
deposits Mixture is too rich. Replace the main jet with the next smaller size.
White or light gray Mixture is too lean. Replace the main jet with the next larger size.
White or gray insulator
with small black or
grayish brown spots
and electrodes having a
bluish-burnt appear-
ance Mixture is too lean. The piston
is damaged or seized. Replace the piston and spark plug.
Tune the carburetors again. Begin with low-speed
tuning.
Melted electrodes and
possibly a blistered
insulator
Metallic deposits on
insulator Mixture is too lean. The spark
plug melted. Check the piston for holes or seizure.
Check the cooling system, gasoline octane rating
and ignition timing. After replacing the spark plug
with a colder type, tune the carburetors again.
Begin with low-speed tuning.
Trouble Diagnosis Adjustment
Hard starting Insufficient fuel Add gasoline.
Excessive use of the starter or
choke Return the starter lever to its seated position so
that the starter valve is fully closed.
Fuel passage is clogged or
frozen • Check and, if necessary, clean the fuel tank air
vent, the fuel filter and all of the fuel passages.
• Check and, if necessary, clean the carburetor
air vents, fuel passages and the float valve.
• Clean the float chamber of any ice or water.
Overflow Adjust the fuel level.
Poor idling:
• Poor performance at
low speeds
• Poor acceleration
• Slow response to
throttle
• Engine tends to stall
Improper idling speed adjust-
ment Adjust the engine idle speed.
Refer to “Low-speed tuning”.
Clogged bypass hole Clean the bypass hole.
Clogged or loose pilot jet • Remove the pilot jet, clean it with compressed
air and then install it.
• Make sure that the pilot jet is fully tightened.
Air leaking into the carburetor
joint Retighten the clamp screws on the carburetor
joints.
Defective starter valve seat Clean or replace the starter valve seat.
Overflow Adjust the fuel level.
Poor performance at
mid-range speeds:
• Momentary slow
response to the throt-
tle
• Poor acceleration
Clogged or loose pilot jet • Remove the pilot jet, clean it with compressed
air, and then install it.
• Make sure that the pilot jet is fully tightened.
Lean mixture Overhaul the carburetors.