Hey guy’s, I was reading a thread from a couple days ago where people were listing what their jetting specs were. I was suprised to see a bunch of 450's with 158 mains, and 38 pilot jets. I have a 99 YZ400F, and it's way richer than that. Main 180 Pilot 48 Needle 2nd slot from top Stock pipe with PMB spark arrestor Live at sea level, ride at 3000-6500 ft. My bike runs great. Plug is not rich at all. One of the best starting machines I have ever had. I was tweeking the jetting when I first got it to help make it start easier, and to get rid of that annoying de-acceleration pop at low rpms. Going to a bigger pilot eliminated that minor backfire, and helped starting. My only complaint is the off idle bog when you quickly snap the throttle. I did the throttle pump mod, and shortened the squirt duration from 5 secs to .5 secs. Helped a bit. Did a homemade power now; helped a bit more. I can snap the throttle, and it has a bog, but won't kill the engine as it once did. Adding an 8oz flywheel weight made it better for riding, but also slowed down the quick rev. I wish it had no bog, as my buddies CRF450, but I got tired of tweeking. My question is, how could there be such a huge disparity on jetting between this 400 and the 426/450, and still run so well, minus the bog off idle? I keep my pilot fuel screw at 2.5 turns out. If I screw it in just a turn, it will start popping on de-acceleration just sitting there at idle, so I need to keep it where it is, or go up one pilot jet size. Float is set perfect per the manual. At idle to 1/4 throttle, it's just the pilot, and the needle right? If I went to a different needle, could I drop down the main jet size?