Have you checked the float level yet?
The float's should be sitting parralel to the fuel bowl mounting face with the float tab just toughing the pin in the needle (needle and seat)
If the float level is wrong that will affect the way the bike run's, too high float level and it'll run rich, too low float level and it'll run lean
I don't know why an earth lead would have power to it ?
The bike wouldn't run with it connected to earth if that was the case.
Does your bike have a rubber boot sealing the throttle cable to the top of the carby ?
If not that can also let the carby run lean at different rpm's, especially if it has a worn slide
If you are going to get an Oko for it and keep it a 160cc, i'd go for the Oko 26mm
Yeah that spring loaded bush sit's in the end of the crank and push's onto the inside of the clutch / r/h engine cover
It's shown on page 11 here, part number's 14 &15
http://www.dhz.com.au/assets/usermanual/OUTLAW160R_z160HO_Engine_Diagram.pdf