https://tractionmech8.wordpress.com/2014/04/page/3/ http://urbanemissions.blogspot.com/2009/12/2-stroke-vs-4-stroke-engines.html
Snowmachine manufactures are always trying reduce the weight of their snowmachines as well as increase the horsepower. This is why manufactures usually chose a two-stroke engine. Two-stroke engines do not require many heavy engine components such as a valve train and a reservoir of engine oil in the motor. Also, two-strokes engines have a power stroke every revolution of the crankshaft, which eliminated the need for the large moment of inertia that keeps the crankshaft of a four-stroke spinning between the power strokes every other revolution. This larger needed moment of inertia of a four-stroke engine is established by counter weights that are are far as possible from the axis of rotation of the crankshaft. Overall, four-stroke engines on average weigh significantly more then a two-stroke engine. Also, since two stroke have a power stroke twice as often as a four-stroke, two stroke supply a greater amount of torque then its equivalent displacement four-stroke counterpart.
Intro Traction Sidehilling Horsepower Weight Reduction Bibliography