7 - 8
TUN
* marked: In case of hard breathing, check the carburetor breather hoses for clogging. Closed to 1/4 throttle
Poor acceleration
White smokeUse jet needle with a larger diam-
eter.
Turn in pilot air screw.
Unstable at low speeds
Pinking noiseLower jet needle clip position.
(1 groove down)
Turn in pilot air screw.
Poor response at
extremely low speedReduce 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 speedsRaise jet needle clip position.
If this has no effect, lower the jet
needle clip position.
Poor response when
throttle is opened quicklyCheck overall settings.
Use main jet with a lower calibra-
tion no.
Raise jet needle clip position.
Use jet needle with a larger diam-
eter.
If these have no effect, use a main
jet with a higher calibration no.
and lower the jet needle clip posi-
tion.Check air filter for fouling.
Poor engine operation Turn in pilot air screw.
Adjust the throttle stop screw.Check throttle valve operation. Symptom Setting Checking
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.
SETTING
7 - 9
TUNSETTING
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.
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.
NOTE:
When checking the discoloration of spark
plugs, be sure to stop the engine immedi-
ately after a run and check.
Avoid racing.
When changing the heat range of spark
plugs, never attempt to change it more than
±1 rank.
When using a spark plug other than stan-
dard, check its heat range against the stan-
dard and check that it is a resistance type.
Note that even if the discoloration seems
proper, it may slightly vary with the spark
plug maker and oil in use.Standard spark plugBR10EG/NGK
(resistance type)
5PA70110
