I've had this particular XT500, a four stroke single and my fourth, for about 18 months. It had on a megaphone style race exhaust for the past riding season. Just as it started to get cold here in Idaho, I ditched the pipe for a factory muffler and installed it after I refinished the metal. It was sandblasted and painted and I bolted it on and started it right up. It ran for about 10 seconds, then as I revved it a little, it died and hasn't started for anything again.
![Head Scratch :headscratch:](./images/smilies/headscratch.gif)
My question is, though it has fuel, spark, compression (a recent rings and head job), could the mixture have changed so much by the different flow characteristics that it wouldn't run without another jetting change?
Thanks for your thoughts, fellas.