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3-23 3 Arctic Power Valve (APV) System 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 exhaust valves, return springs, actuating cables, and the servomotor (servo). 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. There is also a vent hose on each APV housing to relieve the pressure of “blowby” gases that may escape from the cylinder. 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 CDI/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 different with each model. 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 Oil. Using oils other than the recom- mended oil may increase the frequency of required cleaning due to increased buildup of carbon deposits. 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. Remove the two bolts securing the servo cover. AP116A 2. Using a small screwdriver, remove the cable retaining cover. APV VALVE POSITION ENGINE MODEL ONE STAGE RPM RANGES Acceleration Deceleration Down Up Down 600 cc Twin 0 - 6999 7250 and Above 6900 and Below 800 cc 0 - 6799 6800 and Above 6300 and Below 600 cc Triple 0 - 6949 6950 and Above 6650 and Below ENGINE MODEL TWO STAGE RPM RANGES Acceleration Deceleration Down Middle Down 500 cc 0 - 6949 6950 - 7199 6700 and Below |