Hi gang, I have searched and read countless threads on this topic and have questions specific to my situation. I bought an 04 wr450 a few months ago so am bit of a newbie. I am not sure what mods were done. My first ride was a month ago where half way through the ride, the stock exhaust insert broke off. So we took it out and I learned what an uncorked bike ran like. No stutter or hesitations that day at all - with or without insert. Last weekend got to ride the bike for a few hours, without insert. My last ride was a medium high speed gravel road where part way into it I noticed a bit of a stutter at constant speed. It was fine under acceleration. The stutter got worse as the ride went on. Then today after cleaning the air filter I took a couple runs up the street and the stutter was very noticeable even on acceleration. (note: the oil on the filter wasn't dry yet so maybe the increased stutter and hesitation was from that?). So my questions: If the stutter was due to jetting without the insert, wouldn't I have noticed the stutter immediately after taking out the insert? Am I missing something else as the cause like clogged carb, bad gas? I am going to get a new aftermarket insert (to quiet it down) so do I wait until I have that installed to fiddle with the jetting? Last question, can I do damage to the engine riding the bike with a major stutter/hesitation? Thanks.