The much acclaimed high flow filter biturbo hoax proves very little to me besides making someone rich. Fine tuning and perfect carburation of these tiny engines enriches max performance. Although I'm going to drill some holes in my car airfilter housing maybe it will go faster.
Somewhere a tiny leak of oily exhaust discolors the pipe.
If it's the exhaust conn. you could use a copper/asbest compression gasket, hard to get in the US.