Had a problem with my SS50 not running well, but it wasn't consistent, mainly in the higher revs but not always and not with a particular throttle position.
Till at some point, I was looking down at the motor again, while riding, I figured out that it was my leg in front of the carburetor disturbing the airflow....
Solution: take of the cheap crappy long velocity stack, and make a nice shorter one, so I get more clearance to my leg.
turned from the top of some old gas bottle
no more ugly rubber ring holding the screen, but a nice internal "filter" to keep out bugs and rocks.