Spark Plug; Carburetor Adjustment - Joyner JNSZ650DLB Owner's Manual And Parts Manual

Harm or damage may occur if use coolant that does not meet the
specification 50% standard green coolant and 50%distill water.

Spark Plug

a. Remove the spark plug and inspect it
each time you change the oil.
(Use a spark plug wrench) The electrodes
should be kept clean and free of carbon.
The presence of carbon or excess oil will
greatly reduce proper engine performance.
If possible, check the spark plug gap
(area between electrodes) using a wire feeler
gauge. This specification is 0.025"~0.030".
b. Before installing spark plug coat threads
lightly with graphite grease if possible,
to ensure easy removal next time the spark plug
needs inspection (see Figure 24).
c. It is advisable to replace the spark plug at least once a year to insure easy starting
and good engine performance.

Carburetor Adjustment

Never make unnecessary adjustments. The factory recommended settings are
correct for most applications. It's not necessary to disassemble the screw unless the
carburetor needs to be replaced. Prepare a 50r/w tachometer before adjustment.
a. Warm up the engine (5~10min)
b. Tighten the air screw gently. Back out 2-3/8 turns counter clockwise (see Figure 25).
c. Connect the tachometer, adjust the throttle to limit the idle speed. The standard value
is (1400RPM).
d. Turn the air screw counter slowly and observe the RPM of the engine, stop adjusting
as the RPM reaches the top speed.
e. Adjust the screw and adjust the idle speed to an ideal value.
f. Repeat step d and e until the rotate speed of engine stables.
Figure 24