Hey.
The real thing here is if the engine sparks or not.
Sometimes we can´t see the spark but it is audible.
I have 3 ryobis working great and all starting by hand. The secret is a proper choke, they liker to start when the carb is filled up with the choke pump that comes in the trimmer.

In a uncowled engine I choke it with a finger until it gets fuel wet, then it starts at first or second flip.

Try it.

Tato Lazo.