2012 yfz cutting out!

[atvnut22]

This isn't my bike it's a buddies so I'll do my best to explain the situation. He bought a 2012 yfz, carbeurated bike. I went with him to pick it up, we asked if their was anything that voided the warranty. The salesman said that anything could be done besides open the motor up. The boy took the baffle out and a few days later it started cutting out and missing on the bottom end. Does the same with the baffle back in. He calls the salesman, and the salesman states that these fourwheelers come stock running too lean. He suggests he bring it in and have the valves adjusted for free. He does, takes it home and it doesn't fix the problem. Long story after that, salesmen denies ever saying any of it, all they will do is put a new spark plug in it and tells my friend he needs to buy a dyno jet kit. So my question is what else could be causing this on a new bike, or if you think its jetting what size jets do we need to put in it? Sorry for the long story, just trying to fill everything in!
Thanks in advance,
Brock

[XCRacer236]

They do run lean from the factory. Mine barely ran when I got it as well.

that salesman must have mush for brains for telling him adjusting the valves on a BRAND NEW bike would fix it running lean.. :huh Not only that, YFZ's don't need the valves adjusted... ever.

Leave the baffle IN. You get no gain from taking it out.

If the dealer wants to put a new plug in it, let them.

Sounds to me like your buddy needed to buy a jet kit from day 1 and left the dealer out of it. Buy a jet kit. Unfortunately tho, I can't help you on what sizes since it's a different Carb than what I have. ;)

[str8shooter]

Valves DO go out of adjustment and DO need periodic maintenace on all yfz450's done,thats why they sell shim kits!Usually the bike gets hard to start and would'nt expect you would need it on a new bike.Jetting should fix the problem or I would be taking it to another dealer for warranty if you don't know what you're doing.I would richen up the mixture screw 1/2 turn and maybe bump up the main jet one size especially if you take the airbox lid off.I'm not quite sure what stock size is on the newer ones but guess 155-160 would be right.Don't waste your money on a full jet kit unless you plan on more changes then I would suggest a ncvq needle and 165 for a pipe and maybe a 45pilot jet.Hope this helps