I've got the above mentioned mod.
I'm running pump gas (premium), so Eric modified the head appropriately too. I run Harescrambles in D-15. Elevation here averages 1000' or so. I'm slightly rich on my jetting with a 168 main, 55 pilot and stock needle (M82 something) in the mid position and an FMF Gnarley pipe and a reed spacer. I've dropped my gearing to 14/51. I find that I spend less time slipping the clutch when the going gets gooey and when the ground is perfect, I can spend most of my time in 2nd & 3rd or 4th. (remember, it's hard to dodge trees in 5th gear!)
This thing is like a tractor on hills. I can just roll the throttle on and off to maintain traction and momentum. The 125 guys are screaming and slipping there clutches to make power and get up the hills. In fact, hills are where this thing excells!! I can just rocket up the knarleyest hills and not look back. I'll top out pretty quick if I have an open field and get it up into 5th, but that doesn't happen often.
