Brass rod upper bushings in a 2 cycle engines are a really bad idea with low oil to fuel premix ratios. This is reason why nearly all small 2 stroke industrial engines use needles and rollers top and bottom. It is because 2 strokes don't have any thrust reversals on the rod bearings so the lubrication film has a chance to renew itself. You would have to run 16:1 to 20:1 mixes for these to last any amount of time.
It's just a bad idea, especialy when used in a really high RPM/performance 2 cycle engine.
Duke Fox of Fox Model Airplane Engines, and one of the 1970's writers for Cycle World explained in detail the reasons why you never find bushings in modern 2 stroke engines any more. And both these articles were written in the 1970's. Needle bearings for the small end of the rod can work reliably for hundreds if not a couple thousand of hours with the fuel-oil mist of a 40:1 fuel ratio in weedeaters and chainsaws.