I agree with wyelde, if it is not noticably low on compression, or has 5000+ miles on it, I will run it til it blows. If you are any good with motors, or have tuned a few snowmobiles, seat time will get you used to how your snowmobile reacts. If something sounds funny, or it is not running like usual, I dont ride any farther than the shop and I fix what is wrong. Not saying that I have always been able to tell, but if the sled has been dialed in, listen to it, and if it responds different and you notice it, dont push your luck.