a discussion of 2-stroke engines

A 2-stroke single cylinder engine is a marvel of engineering, even today. It is such a simple design and offers more lightweight portable power than a more complex 4-stroke of the same size. The piston serves double duty as both the power core, as well as the fuel pump, and even intake and exhaust valves.

animation and explanation

The most complete body of information on the history and theory of the 2-stroke engines I have found so far is https://en.wikipedia.org/wiki/Two-stroke_engine.

Having powered everything from toy airplanes and cars, to over the road trucks and even some small tractors these are the most versatile engines I know of. Since the oil required for lubrication is mixed with the fuel, a separate oil chamber is not required to keep the engine in good condition. This is also one of the downfalls of the 2-stroke engine. Since the lubricating oil is mixed into the fuel, it burns the oil and likely will never pass an emissions test. The other downfall is a lack of low rpm torque like we are used to seeing from a 4-stroke engine.

These days motorcycles, chain saws, weedeaters, leaf blowers and other light weight power tools are the only examples of 2-stroke engines readily available. All of these applications work really well with the high revving nature of the 2-stroke engine. To my ear there is no better sounding engine than a well tuned 2-stroke.

To keep a 2-stroke running as it should takes a bit more effort than a 4-stroke. Hard starting is likely caused by loose bolts and screws, or bad gaskets. These can be carburetor mounting screws, or engine case screws and gaskets. Mixing oil and gas can be troublesome also, but I have learned that a ratio of 50:1 is the best all around mix for all 2-stroke engines you want to last more than a few hours. This is the mix most chainsaws call for, and weed whackers and leaf blowers run really well with this mix too. This is the same mix my mini cultivator calls for. Regular maintenance consists of cleaning the air filter and gapping the spark plug after about 20 to 30 hours of operation. Replacing these parts every year and tightening all the bolts will keep the engine running like new. Preventing engine damage is a simple matter of keeping the cooling fins clean, and using a good fuel stabilizer for todays ethanol fuel blends, along with a known quality 2-cycle oil.

Very helpful, thanks Keith.

Please consider this to be a classroom 12acre. Hubby and I BOTH have problems with 2 stroke engines and hubby has rebuilt car and truck engines before. There are just enough subtle differences to get us in big trouble.

LOL the biggest thing is loose bolts. The lower engine case usually serves as the fuel pump. Forgetting everything else that the piston does for a moment. As the piston moves up in the cylinder it creates a vacuum in the crankcase. This opens a valve and draws fuel in. Then as the piston moves down that simple valve is closed and fuel is pushed into a passage that leads to the other side of the piston (where it is compressed and burned) A loose bolt at the carburetor or around the engine case will cause the engine to run lean or not get enough fuel to run at all.

The carburetors are very sensitive to trash and alcohol content of the fuel. Fuel for most 2-stroke engines sits around a lot. There may be cases where you won't use a full gallon in a season. It is possible for todays fuel (gas) to go bad in as little as 2 weeks. Special fuel stabilizers (I use sta-bil ethanol treatment) should be added to the fuel at the same time you add the oil. Adding 2.6 ounces of 2-stroke oil to 1 gallon of fresh gas for a 50:1 mix seems to be the best all around fuel mix. Adding 1 to 2 ounces of fuel stabilizer to this will not harm anything.

Spark plugs are normally gapped at 0.026" to 0.030", I usually try for about 0.028".

Very informative topic.

Funny most people's biggest problems are loose screws and blown gaskets too!

LOL, funny but true