I'm using 30:1 per the manual. Leaking out of power valve, joint between expansion chamber & mufller & out of muffler. Heard people are using up to 50-1. Doesn't it affect cylinder/piston life substancially? Thinking of cleaning power valve. Don't like Yam. manual particularly the 4 languages. What's the procedure? Do you have to take the head and piston off? I've raced this beast twice (AMA enduro) & its considerably better than my 05 crf250r. Shorter wheelbase, lower CG, tons of power when u want it, surprising torque. Thanks Yamaha (formely known as Honda by the Gages Lake ice racers)Steve.