30
3. Compare the reading with the timing selection in
the chart.
4. If timing and resistance are not within specifica-
tions, replace the switch.
NOTE: Before replacing the switch, repeat the
test to confirm results.
Arctic Power Valve (APV) System
This RPM and exhaust pipe temperature controlled
servomotor (servo) actuation system adjusts the size of
the exhaust ports to provide peak performance
throughout the RPM range.
At low RPM, the exhaust valves are held in the
DOWN position by return springs. This gives the
engine a “low port” exhaust design calibrated to pro-
vide maximum low RPM power.
739-152A
At high RPM, the exhaust valves are raised. This cre-
ates a “high port” exhaust design calibrated to provide
maximum performance at high RPM.
739-152B
To adjust the APV system, use the following proce-
dure:
1. Remove the actuating cables from the servo.
2. While holding the cable housing, lightly pull on
one cable end to remove slack.
3. Measure the amount of exposed cable from the
cable housing to the end of the cable.
0735-516
4. Repeat steps 2 and 3 on the other cable; then com-
pare the measurements.
NOTE: Measurements must be within a range of
35 mm ± 1 mm.
NOTE: The measurements must be equal and
within the specifications. If the measurements are
within specifications, no adjustment is necessary.
If they are not within specifications, proceed to
step 5.
5. Loosen the jam nut on the cable adjuster to be
adjusted; then using the adjusting nuts, lengthen or
shorten the housing as needed.
6. While holding the adjusting nut in place, tighten
the jam nut securely.
7. Install the actuating cables to the servo.
Exhaust Controlled Timing (ECT)
System
This system automatically adjusts the ignition timing
to provide maximum performance through a variety of
operating conditions. The ECM unit receives input on
engine RPM (demand) and exhaust pipe temperature
(engine condition) and adjusts the ignition timing
accordingly. This system is not adjustable and is main-
tenance free.
If a system fault is suspected, disconnect the exhaust
pipe temperature sensor; then use an ohmmeter to
check continuity of the exhaust pipe temperature sen-
sor located in the expansion chamber. A reading of
either 0 ohm or infinity indicates a failed sensor.
Ignition Timing Rotary Select Switch
Timing Selection
ohms
+3
4640
+2
3000
+1
2200
0
1470
-1
1000
-2
680
-3
402
CAUTION
If excessive adjustment is required to attain synchro-
nization, the entire adjustment procedure should be
repeated.
