Echo CS-4920 with 20 Inch Bar and ChainDescription: The CS 4920 features a powerful 50. 2 cc, 2 stroke engine but is the lightest saw in its class. With a purge bulb for easier starts and a momentary switch that returns to the "ON" position when the saw is shut off, the CS 4920 is simple to operate. TOP FEATURES: 50. 2 cc professional grade, 2 stroke engine Momentary stop switch Heavy duty air filter with tool less access provides superior air filtration. Features: Momentary stop switch: