Arctic Cat Sno Pro 120 2011, Service Manual

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THEORY
Two-cycle engines and their exhaust systems are
designed to produce maximum horsepower in a given
RPM range. This RPM range will change according to
how high (or low) the exhaust port is in relation to the
cylinder. Engines designed for racing have a “high port”
exhaust system and will produce more horsepower at
higher RPM but only with the loss of low end power and
overall fuel economy. “Low port” engines will produce
maximum horsepower in the low RPM ranges and pro-
vide good mid-range fuel economy, but they sacrifice top
end performance.
The APV system does not increase engine horsepower,
but it does allow the engine to be designed for maximum
top end horsepower without the losses associated with a
“high port” exhaust system.
735-476B
COMPONENTS
The main components of the APV system are the follow-
ing.
A. Lighting Coil
B. Chassis Control Unit (CCU) (500/600 cc)
C. Voltage Regulator/Rectifier (800/1000/1100 cc)
D. ECU
E. Servomotor (600/800/1000 cc)
F. Power Valve Cables
G. Power Valves
Lighting Coil
The AC current generated by the lighting coil flowing to
the CCU (500/600 cc) or regulator/rectifier (800/1000/
1100 cc) is the power source for the APV system.
Chassis Control Unit (CCU)
(500/600 cc)
The AC current from the lighting coil first enters the
CCU changing from AC current to DC current. Since the
APV circuit cannot use pulsating DC current, it must be
converted (by the CCU) to straight DC current.
Voltage Regulator/Rectifier
(570/800/1000/1100 cc)
The AC current from the power coil first enters the regulator/
rectifier changing from AC current to DC current. Since the
APV circuit cannot use pulsating DC current, it must be con-
verted (by the condenser) to straight DC current.
On those models using the lighting coil as a power
source, AC current enters the ECU from the lighting coil
and is changed from AC to DC current by a rectifier
located within the ECU.
ECU
The computer within the ECU has been programmed to
raise and lower the power valves at a specific engine
rpm. When this rpm is reached, DC current is routed to
the servomotor by the ECU.
Servomotor
The servomotor consists of two circuits. One circuit is a
DC circuit operating the DC motor within the servo, and
the other is a potentiometer measuring the servo pulley
position based on voltage.
The computer within the ECU has been programmed to
operate the servomotor between a low and high voltage
range. If voltage is not within the range, the computer
will shut down the APV circuit. The computer will then
make a total of three more attempts to cycle the power
valves. If the correct voltage or pulley position isn’t seen,
the APV circuit is shut down and no more attempts will
be made until the engine is shut down and restarted.
Exhaust Valve Cables
The exhaust valves are connected to the actuating cables
and, along with the return springs, are contained inside
the APV housing on the exhaust side of each cylinder.
The other end of the actuating cable is connected to the
servo.
OPERATION
At idle and low speed operation, the exhaust valves are
held in the “low port” position by the return spring.
When engine RPM reaches a predetermined point, the
ECU will send a signal to the servo which cycles and
pulls the exhaust valves into the up or “high port” posi-
tion. The RPM that the valves open is different with each
model.
If the servomotor cycles the exhaust valves as explained
above, the exhaust valve circuit is operating satisfacto-
rily. If the servomotor makes no attempt to open the
valves or if the servo attempts to cycle the valves three
times (then stops working), a problem exists and it must
be corrected.
Servomotor Cycles Three Times
In this situation the ECU computer has been programmed
with a voltage range (low and high) that the servomotor
must operate within. If the servomotor is put under too
much load, its resistance goes up and may exceed the
range upper limit. It will then stop and attempt two more
times. If the resistance still is too high, it shuts down.
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