the percentage of oil in the mix depend on the kind of oil you are using.
Some oil like bel-ray which is my favourite can be run at 2%. The use of another kind of oil will require to be run at a higher %.
I found out that any good oil can be run at 3% but not always at 2%. I wouldn’t care about going to 2.5.
If the inside of your exhaust, expecially the end, it appear to be darkish and grease it means you are running rich.
That you are running rich it doesn’t mean you are runn ing with too much oil.
Rich and lean are terms to indicate the quantity of fuel and not the quantity of oil.
So in few word you are running rich means your engine it is getting more fuel that it can completely burn and since use.
For this reason you will have more oil deposit then you should.
So I think either your air filter is a little blocked, and so will make you run richer, or your main jet it is too big.