Change Of The Heat Range Of Spark Plugs - Yamaha YZ85W1 Service Manual

Symptom
Closed to 1 / 4 throttle
Poor acceleration
White smoke
Unstable at low speeds
Pinking noise
Poor response at extremely low
speed
Poor response in the low to
intermediate speeds
Poor response when throttle is
opened quickly
Poor engine operation
* marked: In case of hard breathing, check the carburetor breather hoses for clogging.
Setting
Use jet needle with a larger diameter.
Turn in pilot air screw.
Lower jet needle clip position.
(1 groove down)
Turn in pilot air screw.
Reduce pilot jet calibration No.
Turn out pilot air screw.
If not effect, reverse the above procedures.
Raise jet needle clip position.
If this has no effect, lower the jet needle
clip position.
Check overall settings.
Use main jet with a lower calibration no.
Raise jet needle clip position.
Use jet needle with a larger diameter.
If these have no effect, use a main jet with
a higher calibration no. and lower the jet
needle clip position.
Turn in pilot air screw.
Adjust the throttle stop screw.
9-6
ENGINE
Dragging brake
Overflow from carburetor
Check air filter for fouling.
Check throttle valve operation.
This should be taken simply for an example. It
is necessary to set the carburetor while check-
ing 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.
CHANGE OF THE HEAT RANGE OF SPARK
PLUGS
Judging from the discoloration of spark plugs,
if they are found improper, it can be corrected
by the following two methods; changing carbu-
retor settings and changing the heat range of
spark plug.
Standard spark plug
• In principle, it is advisable to first use spark
plugs of standard heat range, and judging
from the discoloration of spark plugs, adjust
carburetor settings.
• If the calibration No. of the main jet must be
changed by ±30, it is advisable to change
the heat range of spark plugs and newly
select the proper main jet.
TUN
Checking
BR10EG / NGK
(resistance type)