I have a 2007 Yamaha yz450f. I live at 5000 ft above sea level and need advise. I have read some members say the stock jetting setting are a lean setup at sea level. I have used an excel spread sheet that says at 5000 ft and 70 degrees I should be running a 152 main jet, a 42 pilot jet, and the needle setting at 3rd position. I have not tested this new setting but when I had it set to a 152 main, a 42 pilot, and needle at 4th groove I would run lean and have a great amount of back fire on deceleration. I don't want to damage the motor by running lean, so I was thinking of going with a 157 main, 45 pilot and clip position 3 on the needle. Anyone have experience at this altitude with an 07 yz450f? HELP? Grayracer513 are you still around?