Sorry for the delay got busy. But yes timing on a 2 stroke is fixed. If your back firing most comon is a fouling out spark plug. Try a new one and make sure gap on it is right arond .28 " at least that's what I set all mine at." And reeds be sure to make sure they are 100 percent good. A small crack csn create a major issue. Also to much oil will cause problems. The mix has to be within threshold. Too much oil will ruen plugs and put un wanted stress on your motor to little will blow it up. Glad its running better.

 

Plugs good, when I get a sec I'm check reeds. THe timing is not adjustable on pw50, but I have no clue if someone has been into it,