The spring I run on my secondary is white and like I said very easy to set in the mountains, one set back i've been told it wears the buttons off alot faster other than that works well. With u running the sensor off one pipe doe's it give u a accurate reading and can't u put a small shield in front of the sensor if u put it before the y pipe. Haven't put one in before and how hard is it to get at if u have it before the y pipe. With the track I was thinking between a camoplast extreme 162 x 2.5 or go to a 174x2.5 and slide the suspention back about 5.5" This is the way kenny at mountain magic has been doing it on all of the sleds he's been doing. He said some guys have been drop and role their sleds and it works real well but the cost is their also. With putting on a 174 and slide the suspention back it changes the attack angle but drop and role cost is much higher, was also told not to put a 3" track in because it doesn't fit under the tunnel and it tears the tips of the track and turns into a 2.5" track real fast.
Here's a pic of my o2 sensor install. I pic'd here as it's easy to get at to replace. Otherwise it's drilling out rivets or dropping your suspension. Works good here, it's only at 1200rpms it reads lean, as soon as I touch the throttle the readings come down and seem accurate.