For an affordable trimmer (under $200) with the power and the reach to clean up a large yard, look for a 2-cycle machine that has separate primer, choke, and throttle controls for easy starting. Two-cycle engines run on a mix of gas and oil.
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A curved shaft that's easier on the back, with a loop handle for better balance and control. Echo GT-225 curved shaft trimmer; about $160; shop.echo-usa.com