Anyone has experienced that when tune the engine near peak power then everything is fine for few tanks. After a long rest, the engine will be richen and bugging in low rpm, then give it fulll throttle for a while, it will be fine. Then it keeps richen alittle itself in the same tank.

I read from the new plug. The plug is shiny, little bit wet around, but the surrounding is black.

Any best way to tune this engine?