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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.
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| Exhaust
power valve with deposit build-up |
Clean
exhaust power
valve |
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 dealership 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, disrupting 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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Extending time between
cleanings through the use of AMSOIL 2-Cycle Oils
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Monitoring and adjusting
oil consumption as needed
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Cleaning the valves before
they get stuck to allow for easier removal
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Using AMSOIL Power Foam to
loosen the deposits
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