OK, I know you're all sick of these jetting questions. BUT! I've got a 2000 WR400. It's got the airbox lid removed, throttle stop cut to 24mm, grey wire disconnected, YZ timed, and a Thunder Alley pipe on the end of an 2002 YZ header. I live and ride at an elevation of 4500+ ft. Here's how the jetting is set up: Main Jet = #170 Pilot Jet = #48 Jet Needle = standard OBDRS, #2 clip position Pilot Screw = 1 1/2 turns out Recently I've been adding octane booster to my 91 octane pump gas. I do this cuz I've been told that it should help in reducing the plug fouling problems I've been having. Get about 6 - 10 rides on a plug before it's useless. Kinda wondering if this may be hurting the jettin too. Here's my problem. Now that it's gotten a bit cooler, 50 degrees instead of 75+, it's just not running right. It's popping & hesitating around 1/2 throttle. Nothing wrong at all down low or WFO. Just in the middle. Tight single track stuff is just killing me. It's not backfiring just a popping and coughing kinda thing. According to the manual, I should just lean the needle a bit. But cooler temps would normally mean I'd have to richen the mix not lean it. Right? I'm thinking that I probably need a new needle. But which one? I've seen alot of people using E series needles. But again, which one? Anyone know what works good at my elevation? Which clip position? :D Any help would be appreciated.