| They can be called "APV" by Arctic Cat, "RAVE" by | | | | valve movement or leave them stuck in one spot. |
| Ski-Doo or "VES" by Polaris. If you own a 2-stroke | | | | Any of these scenarios will drastically impair the |
| snowmobile made in the last 15 years, the engine is | | | | power delivery and output of your engine. |
| likely equipped with "variable exhaust power valves". | | | | The task of maintaining your snowmobile's power |
| If that is the case, you probably know that you have | | | | valve system is not complicated. Your service or |
| to be quite diligent about their cleanliness and | | | | owner's manual will give specific instructions on how |
| operation. This is one engine component that has to | | | | to remove and clean the system. Be careful when |
| be monitored regularly to maintain peak performance. | | | | cleaning the valves, as you do not want to scratch |
| Variable exhaust power valves are moving devices | | | | or roughen the surfaces. Your manual will also offer a |
| located at the engine's exhaust port. Every brand's | | | | specific service interval and it should be followed |
| variation is there to provide the same essential | | | | religiously. |
| service and that is to vary the height and width of | | | | Once your valves are clean, there are ways to |
| the exhaust port according to engine RPM. This | | | | prevent premature valve depositing. First and |
| vastly broadens the power band. At low RPM, the | | | | foremost is to make sure that your machine is tuned |
| valves are in a closed position which promotes more | | | | correctly. Overly rich carburetor jetting is a major |
| complete combustion. This improves low-end torque | | | | contributor to this malady. Rich jetting will allow too |
| and minimizes unburned gases in the exhaust stream. | | | | much fuel into the combustion chamber and this |
| At high RPM, the valves are wide open which allows | | | | promotes carbon formation. If your sled is fuel |
| for optimum exhaust flow. This enables the engine to | | | | injected, make sure that the system is operating |
| rev freely and produce maximum top end | | | | correctly. Also make sure that your oil injection |
| horsepower. Older systems were actuated by a | | | | system is delivering the proper amount of oil. Perform |
| mechanical linkage which opened and closed the | | | | regular spark plug readings as described in your |
| valves based on engine RPM. Modern systems are | | | | manual. If your plug readings are off and you cannot |
| actuated by electronic servo motors which precisely | | | | determine the cause, contact your dealer. |
| position the valves throughout the RPM range. Before | | | | Another major contributor to power valve depositing |
| the advent of the power valve, engine builders had | | | | is the use of poor quality 2-cycle oil. The cheaper |
| to determine one size and shape of the exhaust port | | | | base stocks and additives used in lower grade oils |
| and exhaust pipe. This predetermined whether the | | | | can be cooked into carbon deposits very quickly. High |
| engine would provide its optimum power delivery at | | | | quality synthetic two-cycle oil is notorious for its clean |
| either the high, mid or low RPM range. The power | | | | burning characteristics and will dramatically lower the |
| valve allows the two-cycle engine to provide usable | | | | rate of deposit formation. Good quality synthetic oils |
| horsepower throughout its operating RPM range. | | | | use sophisticated base stocks and high temperature |
| The modern power valve system has evolved from | | | | additives which are engineered to avoid power valve |
| a number of different variations over the last 30 | | | | depositing. They also have an effective detergent |
| years. Yamaha was the first company to find | | | | dispersant package which will allow for much cleaner |
| success with this concept when they integrated a | | | | operation. When it comes to two-stroke injector oil, |
| variable exhaust power valve system in their | | | | you definitely get what you pay for. Spending a little |
| 2-stroke Grand Prix road-racing motorcycles in the | | | | more on an oil that is specifically engineered to |
| late 1970's. The technology then made its way to | | | | provide clean power valve operation will not only |
| Yamaha's production road and motocross bikes the | | | | improve your engine's performance, it will save the |
| early 1980's. Other motorcycle manufacturers soon | | | | headaches and expense that come with premature |
| came up with their own systems. By the early 1990's, | | | | power valve depositing. |
| virtually all high-performance two-cycle motorcycles, | | | | Snowmobiles operated at low speed and steady RPM |
| ATV's, personal water-crafts and snowmobiles were | | | | over extended periods can also promote deposit build |
| equipped with variable exhaust power valve systems. | | | | up. During this type of operation, the valves maintain |
| Keeping the power valve system clean is of | | | | a stationary position and this allows deposits to form. |
| paramount importance. As power valves are located | | | | If the valves are constantly changing positions, there |
| directly in the stream of the exhaust flow, carbon | | | | is less chance of deposits forming and increasing in |
| deposits can accumulate on the valves over time. | | | | size. |
| The deposit build-up can alter the shape of the | | | | Variable exhaust power valves have revolutionized |
| valves and change the engine's exhaust flow | | | | the capabilities of 2-cycle engines. With a little bit of |
| characteristics. In extreme cases, the exhaust port | | | | maintenance and care, they will offer trouble-free |
| can become completely clogged and expensive | | | | performance. |
| damage can occur. Deposits can also can hinder the | | | | |