Re: spark plug half black and half grey
Go back one notch. That is about right for good durability vs. power.
It should pull clean under acceleration and four-stroke a bit when loafing along.
Further tuning will not give much more power, but can easily go too far and cause trouble if you are not experienced reading plug chops.
Be aware you can destroy any two-stroke in short order running too lean.
Err on the side of caution for a happy durable chinagirl!
If more is better, then too much is just enough.
If you can't afford it, build it yourself.