Two Stroke Vs. Four Stroke Weed Eaters

Engine Basics

• A four-stroke engine burns air and gas in the cylinder, pushing the piston outward in a power stroke. The piston returns then discharges burned gases on a second outward stroke, taking in fuel on the second return. It then fires another power stroke. The crankshaft, therefore, turns twice for each power stroke. A two-stroke engine pushes out burned gases on the power stroke and takes in air and fuel on the return stroke, requiring just one turn of the crankshaft to deliver power.

Two-Stroke Advantages

• Two-stroke engines are easier to start in cold weather, and they are lighter. They are cheaper than four-stroke engines and produce from 20 to 60 percent more power for the same weight.

Two-Stroke Disadvantages

• Two-stroke engines use more gas for the same running time as a four-stroke engine, and they are noisier. You have to mix oil with gas to run a two-cycle engine. Two-stroke engines run at higher temperatures and release up to 30 percent of the unburned mixture of fuel and oil as exhaust smoke. When they get older, they emit even more smoke. Since two-stroke engines rely on oil in the fuel to lubricate them instead of having a lubrication system, they wear out more quickly. The oil that you add to gas for two-stroke engines is expensive, and you have to add 4 ounces of it for every gallon of gas.

Four-Stroke Advantages

• Since four-stroke engines have a built-in lubrication system, you don't have to mix oil with gas as you have to do with two-stroke engines. The lubrication system of four-stroke engines helps make them run cleaner, and they more easily meet EPA air pollution standards. They run quieter so are less of an annoyance to your neighbors. They also last longer than two-stroke engines.

Four-Stroke Disadvantages

• Four-stroke engines are generally heavier, a disadvantage in a weed trimmer that the operator has to carry. They have less power for their weight than two-stroke engines. Four-stroke engines also cost more than two-stroke engines.