I'm surprised that a simple clip change would make that big of a difference. When I had 2S (and I've had plenty!), it seemed that 2-3 main jet sizes and 2-3 needle positions would all would work reasonably well. Sure, one specific combination worked slightly better than the next, but only slightly. I had to be really off on jetting to foul plugs.
Sometimes it sure seemed to me that fresh filter oil caused some of my fouling issues. I noticed on my KX125 that I only fouled plugs when starting the bike for the first time with fresh Maxima oil on the filter. When I switched to NoToil, I never fouled again. On my YZ450F, I used Maxima once on the original filter while waiting for some new Twin Airs to show up. Guess what? Fouled a plug! On a 450F?! Switched to NoToil, have 30 h. on the bike, never fouled again. Maybe I was using too much of the ultra-sticky Maxima...dunno.
But, I'm happy for you. :)
