i found out that if when you go to mix your fuel, if you put in about 4 ounces of STP Octane Booster (99cents store stuff) it will make a considerable difference in mid-to high RPM's.
That would be the case if you are running too rich...the octane booster "thins out" the fuel for the fuel/oil mix, thereby making a rich(er) engine lean out closer to peak performance.
Higher octane is pointless to the china in frame engine since the compression is already very low.
Another thing about octain boosters is they can clean the carbon out thus improving the availible oxygen in a given motors combustion chamber, like fuel induction cleaning. Not much experimenting can be done on these chinas, danger will robenson.