Well, over this weekend, I took my kx out to a local strip (bucklebearies (aka Glamis of the east coast)). I decided I'd pick up a barrel of C12 to see if any diffrenece was made.
Well, after dumping a new car's worth of money into a toy I thought I'd give it a shot. Well, I filled the tank with 93 pump mixed with Bel-Ray MC1. Warmed it up and took a few drags (1/2 mile dirt strip), oh yeah, it's fast with that new pipe, it's got quite a load of bottom end, but the top-end screams. So, during a drag, getting to the load of 5th gear, I noticed alot of spark knocking and pinging. After I clutched and started to slow down I noticed it surged a bit and was keeping a not-very noticeable rev. So, after running about 5 more runs and a few trail rides I thought I'd try a tank of C12 mixed /w Klotz Super Tech @ 36:1. Fired up and took it out to the strip. Lined beside a few supermodded Banshee's, Raptors, 400exs, XR650, a few 250's and 450's and a KTM 520. Well, time came and the KX hooked up keeping side by side with the 520, and about an 1/8th way through the drag my KX quite left everything in the dust. *not too bad for a 14 year old bike. The only bike remotely was the XR. But, I beat him by about an 1/10th mile. Fun fun. Anyway, the C12 made a huge diffrence in the top-end, no spark or pinging, and no reving or surging after a drag. But, was it still worth $9.5 a gallon? For a few weekends, yes, but not for everyday trailing. Good for WFO riding, but worthless for trails.
Just my experience.