So, I've asked this a few times but, don't get many comments. I'm gonna try again and ANY comments or suggestions are appreciated.

I've got an '04 yfz450. Runs great, very smooth power delivery with plenty waiting to be released at a push of the throttle. Problem is and has been since I bought it is that at high revs it cuts out. It's like someone flips the key off for 1-2 seconds then flips it back on.

It's not the rev limiter because when it levels out I can go up another 500rpm's before limiter would kick in. I've changed the plug. I'm running a dj160 main up from dj145 with lid off.

Is it possible the valve springs weak and not closing valve's fast enough? Heard weak springs common prob on atv's.

Any ideas anyone. I'm at a loss on this.

 

Have you check all of your electrical parts? I have seen coils(on older models cause this kind of problem(not sure if the 450 has a coil or not) But possibly the CDI box.

It could be possible that weak springs could cause a problem at high rpms.

 

It might be getting scared of all those Warriors that will go 180 mph.

 

Seriously, if the valves were not closing it would either backfire or spit back through the carb, and if it was bad enough the piston could actually hit the valve and you would be done. And if the valves were not closing good seems it would get even worse with higher revs. I would look more closely at the electrical.

 

<div class="FTQUOTE"><begin quote>Originally posted by: Raptor450

It might be getting scared of all those Warriors that will go 180 mph.</end quote></div>

That is possible! Haha!

Thanks guys, I was inches away from buying a cdi off ebay a few months back but, needed someone confirm that possibility and couldn't get it.

It makes since what your saying about the valves. I'm not getting any backfire or spit back so thats not likely. I'll start with the electronics.

Thanks again. I'm ready to get this thing in top shape for the summer. I mean without that little prob it'll probably do like 180mph!

 

Have you checked the tps? Use a analog scale type ohmeter, the digital ones are hard to interpret. Hook up the ohmmeter, and run the throttle thru its full travel, if theres a burp or hick up, it could be the problem. Easy to check and easy to eliminate if thats not the problem.
Then dont forget to check the initial set point too.

 

I had a bad coil do this, I'd give that a try

 

<div class="FTQUOTE"><begin quote>Originally posted by: Koopa

So, I've asked this a few times but, don't get many comments. I'm gonna try again and ANY comments or suggestions are appreciated.



I've got an '04 yfz450. Runs great, very smooth power delivery with plenty waiting to be released at a push of the throttle. Problem is and has been since I bought it is that at high revs it cuts out. It's like someone flips the key off for 1-2 seconds then flips it back on.



It's not the rev limiter because when it levels out I can go up another 500rpm's before limiter would kick in. I've changed the plug. I'm running a dj160 main up from dj145 with lid off.



Is it possible the valve springs weak and not closing valve's fast enough? Heard weak springs common prob on atv's.



Any ideas anyone. I'm at a loss on this.</end quote></div>

Hey, I had the same problem last year with my YFZ 450. Somehow my CDI went bad. Once i got new one, I havent had any problems since. Good luck man

 

<div class="FTQUOTE"><begin quote>Originally posted by: EricWeber
Hey, I had the same problem last year with my YFZ 450. Somehow my CDI went bad. Once i got new one, I havent had any problems since. Good luck man</end quote></div>

Sweet, so thats 2 for CDI which I somehow questioned before for some reason as I said. I'll start there and then move through electronic components.

Thanks guys.

 

Update. Got great deal on ebay for a used CDI. Swapped out this weekend and fixed the prob!

Thanks for the help guys!