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A Look at Snowmobile Exhaust Power Valves
Mounted in the exhaust port of certain snowmobile models, exhaust power valves are devices designed to improve combustion efficiency at varying RPM. Improved efficiency increases horsepower and lowers exhaust emissions.
At low RPM the valves are in a closed position, allowing for more efficient combustion and minimizing the levels of unburned gases escaping down the exhaust port. At high RPM the valves are in an open position, allowing the motor to breathe more freely and improving the scavenging effect needed for efficient performance in two-cycle motors.
Because exhaust power valves are located in the direct stream of exhaust flow, deposits consisting of soot, carbon and ash quickly accumulate, requiring the valves to be cleaned regularly. If they are not cleaned, they may get stuck, and operators will notice a considerable power loss and/or bog-type operation.
In some instances, deposit build-up may be worse than others. There are several reasons for this:
The machine may be consuming more oil than is needed. Oil injection pumps vary the amount of oil injected based on the throttle position. As the throttle is opened, oil consumption increases. AMSOIL 2-Cycle Oils are recommended for use at 50:1 mix ratios, but if the sled is consuming more than one quart of oil per 12 gallons of gas, it is exceeding an average mix ratio of 50:1. The less oil the sled burns, the fewer the deposits that accumulate on the exhaust power valves. If you wish to have a sled's oil injection pump setting checked, AMSOIL recommends bringing it to a local dealer-ship so a qualified snowmobile mechanic can make the correct adjustments.
Another contributing factor to excessive deposit build-up is riding style. Snowmobiles operated at low speeds and/or steady RPM for extended periods of time will accumulate deposits more quickly than snowmobiles operated at higher speeds. Two-cycle motors do not operate at maximum efficiency at slower speeds, causing a large percentage of unburned fuel and oil to exit through the exhaust. This unburned material accumulates on exhaust valves and forms deposits. Also, since snowmobiles operated at low-level constant RPM do not frequently actuate the valve, it allows deposits to form more rapidly, requiring more frequent valve maintenance.
Snowmobiles run at higher RPM operate more efficiently and can extend time between valve cleanings. Efficient operation results in increased combustion temperatures and more complete burning of the oil/fuel charge. Higher RPM also means the exhaust power valve is more frequently actuated, disrupt-ing deposits and slowing down their accumulation.
Finally, the type of two-cycle oil used in a snowmobile can improve valve cleanliness and extend maintenance. Because they effectively fight deposit formation, AMSOIL Synthetic 2-Cycle Oils exhibit better overall performance than petroleum two-cycle oils. AMSOIL Synthetic 2-Cycle Oils also resist friction and heat more effectively, burn cleaner and can safely be used at 50:1 mix ratios.
Routine maintenance is important for snowmobiles equipped with exhaust power valves. However, maintenance can be eased through the following:
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