Snowmobile Arctic Cat 2-Stroke (2007 year). Manual - part 55

3-23

3

741-635A

742-209A

0735-516

The Arctic Power Valve (APV) System adjusts the size

of the exhaust ports to produce maximum horsepower

on the top end while providing excellent low end

power and increased touring fuel economy.

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 horse-

power 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 provide 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 maxi-

mum 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 fol-

lowing.

A. Lighting Coil

B. Chassis Control Unit (CCU)

C. ECU

D. Servomotor

E. Power Valve Cables

F. Power Valves

„NOTE: On these models, the traditional regulator/
rectifier has been replaced by a chassis control
unit.

APV CABLE LENGTH 

ENGINE MODEL

CENTER ± 1 mm (0.039 in.)

600 cc

36.0 mm (1.417 in.)

800/1000 cc

35.0 mm (1.377 in.)

F-Series

Crossfire/M-Series

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Lighting Coil

The AC current generated by the lighting coil, which

flows to the CCU, is the power source for the APV

system.

Chassis Control Unit (CCU)

The AC current from the lighting coil first enters the

CCU which is then changed 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 which is necessary for the APV

system.

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, which operates the DC motor within the

servo, and the other is a potentiometer, which mea-

sures 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 com-

puter 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.

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 con-

nected 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 will cycle

and pull the exhaust valves into the up or “high port”

position. The RPM at which the valves open is differ-

ent with each model.

If the servomotor cycles the exhaust valves as

explained above, the exhaust valve circuit is operating

satisfactorily. If the servomotor makes no attempt to

open the valves or if the servo attempts to cycle the

valves three times (then stops working), there is a

problem and it must be corrected.

Servomotor Cycles Three Times

In this situation the ECU computer has been pro-

grammed 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.

If the servo is commanded to move but the potentiom-

eter output voltage does not change, an error occurs

and the check engine light will flash a trouble code.

Improper servomotor position sensing is normally

caused by one or more of the following:

A. Incorrect exhaust valve cable length (too long

or too short).

B. Exhaust valve cable(s) sticking, broken, or dis-

connected at pulley.

C. Exhaust valves sticking.

D. Exhaust valve spring(s) weak or broken.

Check each of the above probable causes in the order

given to locate the problem of the servomotor cycling

three times in succession; then shutting down.

Check for correct exhaust valve cable length specifica-

tions for model being worked on in this section.

Servomotor Makes No Attempt To 
Cycle

If when running the engine the servomotor makes no

attempt to operate, this is caused by one or more of the

following:

A. Bad connection from the wiring harness and

connector from the lighting coil to the CCU, to

the ECU, or from the ECU to servomotor.

B. CCU output (gauge/taillight/APV) is shorted or

open.

C. ECU output to servomotor is too low.

D. Servomotor failure.

„NOTE: For testing individual APV system compo-
nents, see Section 5.

MAINTENANCE

The APV system requires only periodic cleaning and

cable adjustment. The cables should be checked every

1000-2000 miles and adjusted as necessary. To ensure

maximum performance and minimize maintenance

requirements, Arctic Cat recommends using Arctic Cat

Synthetic APV 2-Cycle Oil. Using oils other than the

recommended oil may increase the frequency of

required cleaning due to increased buildup of carbon

deposits.

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CABLE ADJUSTMENT

Proper cable adjustment is critical to the operation of

the APV system. While it is recommended that the

cable adjustment be inspected every 1000-2000 miles,

the cable should not need adjustment often. To check

the cable adjustment, use the following procedure.

1. On the Crossfire/M-Series, remove the two cap

screws securing the servomotor cover.

FC004

2. Using a small needle-nose pliers, remove the ser-

vomotor retaining clip and the cable holder.

CM126A

CM127

3. Rotate the servomotor actuator counterclockwise

to loosen the cable; then pull the cable housings

down and out of the servomotor.

CM123A

4. Slide each cable drum out of the slot of the servo-

motor actuator.

CM124A

„NOTE: Before proceeding with the cable adjust-
ment, ensure that the exhaust valves are free to
move.

5. While holding the cable housing firmly, pull the

cable as far out as it will go; then release. Repeat

three to four times. The cable/exhaust valve

should move freely without binding. If the cable/

exhaust valve does not move freely, the exhaust

valve assembly will need to be removed for further

inspection.

„NOTE: When measuring the cables, they are to
be routed and as close to their installed position
as possible.

6. While holding the cable housing, lightly pull on

one cable end to remove any slack.

7. Measure the amount of exposed cable from the

cable housing to the end of the cable.

„NOTE: The two cable measurements must be
equal in length or less than 0.5 mm (0.020 in.) dif-
ference in length from each other.

„NOTE: Repeat steps 6 and 7 for each cable; then
compare the measurements to the appropriate
chart.

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„NOTE: The measurements must be within the
specifications from the chart. If the measurements
are within specifications, no adjustment is neces-
sary. If they are not within specifications, proceed
to step 8.

8. Loosen the jam nut on the cable to be adjusted;

then using the adjusting nuts, lengthen or shorten

the housing as needed.

9. Once the proper length has been attained, hold the

adjusting nut in place and tighten the jam nut

securely.

10. Place the cable housings into position in the servo-

motor. Secure the cable housings with the cable

retaining cover.

11. On the Crossfire/M-Series, place the servomotor

cover into position; then secure with two cap

screws.

„NOTE: If for any reason the pulley was removed
from the servo, make certain to align the space
between the two cables with the mark on the shaft
of the servo.

MS401A

REMOVING/DISASSEMBLING

„NOTE: To avoid a parts mix-up, it is recom-
mended that only one valve assembly at a time be
removed from the engine.

1. Remove the valve assembly from the engine.

FC115

CM147

2. Remove the retaining screw securing the exhaust

valve to the valve stopper.

FC112

3. Hold the valve stopper securely and pull the cable

back and up until it clears the top of the stopper;

then slowly release the cable and remove it from

the valve stopper.

FC113

Cleaning and Inspecting

1. Remove all carbon deposits with solvent and a soft

abrasive such as a Scotch-Brite pad.

2. Inspect all parts for nicks, burrs, or other signs of

unusual wear.

Replacing Oil Seal

1. Carefully pry the seal up from beneath taking care

not to damage the valve plate.

600 cc

800/1000 cc