Yamaha RX10K, Supplementary Service Manual

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2-57
CARBURETOR TUNING
INSP
ADJ
Main jet selection chart
Spark plug color Diagnosis Remedy
Light tan or gray Carburetors are tuned
properly.
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
appearance 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.
Troubleshooting
Trouble Diagnosis Adjustment
Hard starting Insufficient fuel Add gasoline.
Excessive use of the
starter or choke Return the starter lever to its seated posi-
tion so that the starter valve is fully closed.
Fuel passage is clogged or
frozen
S
Check and, if necessary, clean the fuel
tank air vent, the fuel filter and all of the
fuel passages.
S
Check and, if necessary, clean the
carburetor air vents, fuel passages and the
float valve.
S
Clean the float chamber of any ice or water.
Overflow Adjust the fuel level.
Poor idling:
S
Poor performance
Improper idling speed
adjustment Adjust the engine idle speed.
Refer to “Low speed tuning”.
at low speeds
P
l ti
Damaged pilot screw Replace the pilot screw.
S
Poor acceleration
S
Slow response to
Clogged bypass hole Clean the bypass hole.
S
Slow res onse to
throttle
S
Engine tends to
stall
Clogged or loose pilot jet
S
Remove the pilot jet, clean it with
compressed air and then install it.
S
Make sure that the pilot jet is fully tightened.
stall
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.