They may be called “APV” by Arctic Cat, “RAVE” by Ski-Doo, or “VES” by Polaris. If you own a 2-stroke snowmobile made in the last 15 years, the engine is likely equipped with “variable exhaust power valves”. If that’s the case, you probably know that you have to be pretty diligent about cleaning and running it. This is an engine component that needs to be monitored regularly to maintain peak performance.

Variable exhaust power valves are moveable devices located in the exhaust port of the engine. The variation of each brand is there to provide the same essential service and that is to vary the height and width of the exhaust port according to the RPM of the engine. This greatly widens the powerband. At low RPM, the valves are in a closed position which promotes more complete combustion. This improves low-end torque and minimizes unburned gases in the exhaust stream. At high RPM, the valves are fully open, allowing optimal exhaust flow. This allows the engine to rev freely and produce maximum peak power. Older systems were powered by a mechanical linkage that opened and closed the valves based on engine RPM. Modern systems are driven by electronic servo motors that precisely position the valves throughout the RPM range. Before the advent of the power valve, engine manufacturers had to determine a size and shape for the exhaust port and tailpipe. This determined whether the engine would provide its optimal power delivery in the high, mid, or low RPM range. The power valve allows the two-stroke engine to provide usable horsepower throughout its operating RPM range.

The modern power valve system has evolved from a number of different variations over the last 30 years. Yamaha was the first company to find success with this concept when it integrated a variable exhaust power valve system into its 2-stroke Grand Prix racing motorcycles in the late 1970s. production road and motocross motorcycles from Yamaha in the early 1980s. Other motorcycle manufacturers soon came up with their own systems. By the early 1990s, virtually all high-performance two-stroke motorcycles, ATVs, personal watercraft and snowmobiles were equipped with variable exhaust power valve systems.

Keeping the power valve system clean is of paramount importance. Since the power valves are located directly in the exhaust flow stream, carbon deposits can build up on the valves over time. Deposit buildup can alter the shape of the valves and change the exhaust flow characteristics of the engine. In extreme cases, the exhaust port can become completely clogged and costly damage can occur. Deposits can also make it difficult for the valve to move or leave them stuck in one place. Either of these scenarios will drastically affect the power delivery and output of your engine.

Maintaining your snowmobile’s power valve system is not a difficult task. Your owner’s or service manual will give you specific instructions on how to remove and clean the system. Be careful when cleaning the valves as you don’t want to scratch or scuff the surfaces. Your manual will also offer a specific service interval and it should be followed to the letter.

Once your valves are clean, there are ways to prevent premature valve deposits. First and foremost, make sure your machine is tuned correctly. Overly rich carburetor jetting is a major contributor to this disease. The rich jet will allow too much fuel to enter the combustion chamber and this promotes carbon formation. If your sled is fuel injected, make sure the system is working properly. Also make sure your oil injection system is supplying the proper amount of oil. Take regular readings of the spark plugs as described in your manual. If your spark plug readings are wrong and you cannot determine the cause, contact your dealer.

Another major contributor to power valve deposit is the use of poor quality 2-stroke oil. Cheaper base oils and additives used in lower grade oils can turn into carbon deposits very quickly. High quality synthetic two-stroke oil is known for its clean burning characteristics and will dramatically reduce the rate of deposit formation. Good quality synthetic oils use sophisticated base oils and high temperature additives that are designed to prevent them from depositing on power valves. They also have an effective detergent/dispersant package that will allow for a much cleaner operation. When it comes to 2-stroke injector oil, you definitely get what you pay for. Spending a little more on an oil designed specifically to provide clean power valve operation will not only improve your engine’s performance, it will also prevent the headaches and expense that come with premature power valve deposit.

Snowmobiles operated at low speeds and constant RPMs for extended periods can also promote deposit buildup. During this type of operation, the valves maintain a stationary position and this allows deposits to form. If the valves constantly change position, there is less chance of deposits forming and increasing in size.

Variable exhaust power valves have revolutionized the capabilities of two-stroke engines. With a little maintenance and care, they will deliver trouble-free performance.