Jetting question

[bradycrawford]

I just got a yfz and it has a full yosh titanium exhaust on it and it does not run right it has a bad dead spot at low rpm's but it cleans out on the top but when you let off the gas it pops. so it has to be lean. So if you know what main, pilot, and the needle setting is supposed to be that would be great. also has foam filter and the lid is on. but can take off. any help would be greatly appreciated thanks

[RingoYFZ450]

Please tell me that you are not running your stock jets with that Yoshi!! The YFZ450 is way to lean right from the factory, regardless is you have a pipe or not you should rejet. The factory jets are Pilot 42, Main 155 and Needle on clip 4. A good setup to run with baffle out and airbox lid off is Pilot 45 Main 168 and Needle on clip 4 airscrew 2.5 turns ALWAYS ADJUST AIRSCREW LAST. Remember Lean is BAD 1200 degree hot air melts aluminium parts over time. Rich is ok you just wont have as much power as a perfectly tuned in machine. No two YFZ's are going to jet the same. You have to find the right jettings for your setup. I can only give you a good starting point. Regardless bump your pilot up to a 45 if it is still at factory. Also start out with a 168 Main and the Needle on clip 4. The first YFZ's that shipped with the Needle on clip 3 "to lean" they all ship on clip 4 now. Ride it after these changes and see how it performs. Most likely you will still need to go up to a 170 Main but slowly work your way up by trying the 168 first. Ride a few times If it pops when you release the throttle at high speeds you most likely have a lean needle. Hope this helps.