i have a 2004 yfz 450. on top it starts popping & sputtering. took it to a yamaha dealer today. they said its the rev limiter. just wondering if any has the problem. yamaha says its fine but i just think im not rev out yet. i had a 400ex before & never hit the rev limiter. any suggestions

 

you jetted correctly?

 

My YFZ pops and stutters only when its cold going to take it to the shop one of these days and figure out whats wrong w/ it

 

You shouldn't be hitting the limiter that easily, what gears are you in when it does this and how much throttle? I got about the same mods you do on mine and i hit the limiter at just past half throttle and in second at about 2/3 and after that It's pretty hard to hit it unless your really riding the gear out prety long. Have you tried gearing it up a tooth on the countershaft after the mods? The stock gearing is pretty low for the mods you have. Good luck!

 

first isnt that bad. second is the wors. third does it also but i havent road it for awile past that gear. it pulls real hard but i just dont think im hitting the rev liminter. i also have the cam mod. the guy at yamaha told me he wouldnt recommend a aftermarket rev box becuast with the cam mod it might make the piston hit the valve if im revving it out that much. i just think the dealer should have some way to check the rpms & tell for sure if its the rev liminter

 

The dealer doesn't know what hes talking about (as usual). The YZ dirtbike revs out to 11,500 stock and has the same timing that the cam mod provides so obviously it's perfectly fine. Why would they make a stock bike like this if a valve was gonna hit the piston? The only bad thing the cam mod does is changes the placing of the decompression pin which causes harder starts sometimes, I've noticed just when it's cold it'll take a while to start. Seems like you just need to find the right jetting...have you got the NCVQ needle yet? if so put it on the 4th clip and throw in a 75 main with it and see where that takes ya.