I have an Stihl MS290 I got used last year. Would barely run when I got it last year. Took carb apart and inner screen was plugged full of sawdust, not sure how it all got in there. Anyway, got it running decent, then stumbled across doing a muffler mod to help it run better, then tuned accordingly. IT runs good but after running for 10-15mins, it starts shutting down on me, bogging and then dying. I thought I fixed it and it appeared to be a vacuum lock with the gas cap, relieved pressure, but still will not keep running. I've played endlessly with fuel screws, but can't seem to keep it running right. It has fresh made gas in it too.
Did I screw it up with the muffler mod ( drilled holes in the restrictor plate)?
Should I clean carb again?
I've got 5 chainsaw and can't get any of them to run