After installing the Ti4 slipon on my '04 WR450 (beware, you have to use the quiet core insert, or at least the 1.5" cap insert to keep surrounding property owners and other riders from shooting at you), I had to open the fuel screw by a half-turn to get the idle and off-idle mixing right. No problems, bike ran great for several hours on three seperate weekends, but suddenly, yesterday, she started popping severely on decelleration and stalling, even some nasty backfires. I thought, &%$#@!? Clogged jet? When I got back to base, I found the stock fuel screw had fallen out of the carb and was just barely sticking up into the hole and resting on the starter motor. Dang, I'm glad it was still there, or my riding would have been done for the day. When I reinstalled it, I found the tension spring wasn't even contacting the screw at two turns out, at least I couldn't tell if it was. So, I pulled it out and stretched the spring out and twisted the screw about 2 turns IN from unthreaded (tuning by ear), because I didn't want to smash down the spring again. Good 'squeak-age' from the tension spring this time, so it should stay put until I get the Zip Ty screw from the dealer. The Ti4 pipe looks great (blue-purple annodized), wwaaaaaayyyyy to loud in stock form, but does seem to improve performance slightly over the uncorked stock pipe and saves several pounds from stock. If I need it quieter, I use the quiet core insert, but for most riding, I use the 1.5" cap insert, solid bark, but not too loud for my private property riding areas.