RE: Question about gas to oil mixture........
The oil rate should be as recommended by the manufacturer.
Most of the oil is wasted in order to some of it to reach and lubricate the vital points.
However, the manufacturer has taken that into consideration for the proper cooling of the engine, since the wasted oil cools it down.
For way too much oil, the spark plug would show much carbon deposits.
When the engine and carburetor are cool, the mix has more air and less fuel (cool air is denser and fuel condensates on the cold metal surfaces), hence it is leaner.
When the engine warms up, the situation reverses, and the mix moves to the rich side.
For that reason, the engines should be tuned while warm.
It seems to me that the low end of your engine is too rich, interfering with the transition.