If I got 26x2.125 rims and put some bigger tires on, but also got the advanced sprocket adaptor, would I be able to run them without the chain rubbing on the tires?
What's bigger tyres?
the fattest tyre I can run with a straight chain line would be a 26x2.1.
Otherwise you need to offset your motor, or run a jackshaft as far as I can see.
What's the advanced sprocket adaptor?
With the 2 strokes, there is very little room for adjusting the chain line. A few guys have run 2.3's with bmx chain. The narrower bmx chain clears the fat tires on some frames.