system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do some small engines (like my lawnmower) take 100% gasoline while others (like my weed whacked) require a special mix for fuel?
gpt
2 stroke engines require gasoline-oil mixture

4 stroke engines do not.

The reason is that 2 stroke engines are much simpler such that the oil mixed in the gas will reach all the important parts that need lubrication. 

A 4 stroke engine is much more complex. Oil needs to get places that a gas/oil mixture would never reach. So they design an oil system to manage that.