My 04 yfz just started to run rough this weekend at the track. Its sounds like its skipping and popping and stalls when i go to jump. It has the lights takin off. Ive cleaned the air box carb changed the plug, nplugged the tps and still the same result. wold the valves cause this or maybe the stator? this is my first yfz450 so im lost... Plz any ideas!!!! thx.
P.S. it has gas and the oil is fine..  

yes the timing and valves could be the issue.
as well as a weak stator.
but have you tried to adjust the fuel/air mixture yet?  

Thanks I will check the air fuel screw tomorrow, i also ran a check on the stator using a multimeter im new to using them but i think i got it right I used the one that looks like an arrow pointin at a speaker
->+))) kinda like this The pick up was around 298 and the charging was 0 and made it beep. that means its failing for continuity right? Sorry im new to electrical work..lol!!!  

are you sure you got the right wire?

you'll have the pickup then you'll have the wires for charging, a ground and a lead wire.
the coil lifts the ground when the magneto passes the pick up.
so it's reverse from what you'd think. the the stator doesn't break the electricity or power lead to the coil, it lifts the ground. so make sure you are testing the right wire.  

is it only crappin out coming on the throttle from a low rpm, or just run and idle rough while sitting also?

the mixture and depending on what carburation you have, accelerator pump are culprits there.  

ok i followed the repair manual for the pick up coil it said to go positive to white wire and negative to red wire and i got 298. charging coil it said to go positve to white wire and negative to ground which i got .004 and the beep. It idles fine but at 1/4 and on it pops and skips horrible. Im putting a video of it on my myspace site cause i dont know if you can here. heres the link::  http://www.myspace.com/customcreed
its in my video section titled crappy running yfz.....lol! Sorry its not the best but hopefully it will work  

Ok, may have found the issue. Decided to check the valve clearence and while getting it to TDC i had both dots on the cams to the outside (no cam mod yet) and i noticed the  "I" mark is ahead of the crankcase covers notch by maybe an 1/8" or so they should line up right.
You have the side ways I then the notch the notch should line with the covers notch and the cam dots right?  P.S. new plug was black and wet and only started a couple times.  

did you figure out what was wrong I just put a HMF slipon on my 05 and it was perfect for the first 4 hours and today the damn thing started dying as I would get on the throttle but idled perfect I'm leaning toward the accelerator pump?  

hey wolf1 been reading on here few days and you seem experienced with the yfz-450. I have a 06 with gytr slip on jet kit and no airbox lid, month or so ago baffle blew out of the pipe and other day i raced my buddies honda 450 i usually put two wheelers on him till i top out, i couldn't even top out and we were dead even and he started pulling away up top, i used to smoke him. it is also blowing flames on deceleration and if i hold it like half throttle it is popping and banging, but starts right up fine and rides good, just don't have the power it had up top and is popping and banging blowing flames. used to be able to get right through all gears and top out at rev limiter in 5th but can't even get there now. how does this air fuel screw work turning left and right. which way is left and right i mean please give an example of which side to be on and what is left and what is right. thanks
my guess is its running rich but i don't know why all of a sudden, especially with weather getting colder?, wouldn't it lean out with colder weather or no? it is def. bogging up top and not cutting out. but not smoking or anything, idk. thanks  

You might want to replace your baffle and packing, and reinstall your air box lid. While youre at it, check your valve clearance. The air box lid can have holes drilled in it to help w/ air flow, but you should have some resistance.
The baffle being out will burn up your valves. Get back to smoking that 450R.