need help

[jamienlogan]

My brother has a 08. When he bought it it had a yoshimira full system. We have tryed about every jet set up we can. After it warms up wich is not long it cuts out and has no sweat spot in the gas, it does the same thing on every jet. We also took a carb off of another yfz and same thing. Then we took the pipe off and went back to stock and same. Now we are looking at valve adjustment but it is not looking bad. Any help would be great.

[mxpimp2000]

you should start ur jetting around 45 pilot and 168 main. do the ziptie mod and remove air box lid. a uni or K&N ur preference is an improvement. do the cam mod while u got the valve cover off.

[quadrider2112]

After all u said and the fact that it does it in stock form. I wood say check out ur electrical. I maybe way off but bet its ur stator or pickup coil.

[2002TRX400ex]

i had the same problem most likely your coil pack is bad and there really is no way to test them but if you have another 450 that is running good switch it out they start messing up as soon as the motor gets hot when they are bad.