The leaner oil mix does need to be jetted leaner for sure as it increases the amount of fuel by a pecentage, depending on ratio. Its mixed by the gallon, you have a gallon whether its 24:1 or a 100:1. The 100:1 is more fuel & less oil you lean it out due to more fuel being there to burn.
Any watch kx500 youtube videos. Listen to the sound, "Most" people dont rev them. The moment the powervalves start to open, shift. They should mix 100:1.
When you pull your motor down look at the width of the oil band in the bottom of the case, all the drainback from whats coated your parts. Thank for the tip on this by the way, you know who you are.
This pool, or the oil retained is what loads up & fouls plugs if your running to rich of oil ratio. Like when you let your girlfriend drive it & then you have to "blow it out" cause shes not spinning it high enough to match the load to the oil mix ratio. Ideally you'd have 100:1 at idle, 50:1 when the powervalves open, 32:1 @ WOT & if WOT is sustained for more than 30 seconds the ratio drops to 24:1. Like the chart posted on maxima, mix being rpm / load based you need to figure it on your rpm range. A track bike being one end & a dune / desert bike being the other.
Sounds like it would help if people posted mix ratio & type of riding as well, plug life, & time hours between rebuilds