The fact is . . . The engine was part of a trade and you're not sure what it is? And what is important is that it flies the plane and you are having fun.

The Poulan and Homelites like this were made different 10-15 yrs ago than they are now. These brands are still made today but they are a different design. In fact, now the Poulan, McCulloch, and Homelite in 46cc are identical except for the color.

Some important identifying features of the engine are that it has what's called a bolt on carb and was not one that had the carb mounted in the chainsaw case with a rubber bellows connecting the carb to the engine like they are today. The other important feature is that the coil originally fastened to the cylinder on this engine and was not mounted in the chainsaw case.

Some other facts about the engine was that these designs were typically from 33 to 50 cc. What rpm it turns what prop might be the best judge of what size it is?

There were probably more 42cc engines made than the other sizes?