Can you make a 08 yz run like a 08 kx?

30 replies to this topic
  • silvy423

Posted October 18, 2010 - 09:38 AM


Just bought my 08 YZ450 as a left over at a crazy price so I'm happy about that but not too crazy about the motor at all. I swapped out the stock exhaust for the PC Ti-4R, stock CDI for the 06 version, jetted it to perfection, went up to a 50 tooth rear and it still will not come close to running with that KX! So question is do I spend the money on a 06 exh cam or just look to buying a H/C piston? Should have never ridden That KX now I know what Im missing

  • grayracer513

Posted October 18, 2010 - 10:00 AM


I think that you would be pretty startled if you were to run a KXF head-to-head with your YZF as it is now. I used to hear this about the '06 vs. the earlier YZ450's, and it was the same thing; the '03 was so much stronger. The reality was that on pavement, side by side, the '06 was just as quick in 2nd and third, and stronger from 4th on that the '03 was, in spite of what the butt dyno said about it.

  • silvy423

Posted October 18, 2010 - 11:52 AM


Rode them back to back on the track this past weekend, the KX makes the YZ feel like a 250f. The YZ needs something to wake it up, question is what and how? I like the bike it's just a dog.

  • YamaLink

Posted October 18, 2010 - 12:11 PM


I have a totally stock 08 KX450F, and you are right: the seat of pants impression (which means squat in real riding) makes me think the Kawi is on steroids even compared to a nicely modded 08 YZ450F.

Have you taken lap times?

  • silvy423

Posted October 18, 2010 - 01:22 PM


I don't have to ride the Kawi nearly as hard as the YZ to get around the track. The thing pulls like a 450, my YZ needs some words of encouragement to get going. Just not right.

  • Family Man

Posted October 18, 2010 - 06:14 PM


What altitude and jetting are you running, just curious.

  • silvy423

Posted October 18, 2010 - 06:37 PM


162 main, tried 165 but was a little rich up top, 48 pilot, 2nd clip on needle, stock leak not sure on elevation Phoenix, az

  • Family Man

Posted October 18, 2010 - 08:16 PM


try the fourth clip on the needle. May help.

  • silvy423

Posted October 18, 2010 - 09:46 PM


I would need something far more serious then jetting to get that kind of power out of a yamaha

  • blakers213

Posted October 19, 2010 - 04:55 AM


After your mods on the yamaha your horsepower are probably very close to the Kaw. It is the difference between smooth power verses the kaw not having smooth power. I have read my reviews on the Yamaha and they all say it feels slow but when they compare lap times the Yamaha turns the faster lap times. Yamaha purposely made this bike smooth as silk in the power delivery, it seems to be a mistake because everyone complains about it.

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  • silvy423

Posted October 19, 2010 - 08:48 AM


Huge mistake, this leaves me with buying a 06 exh cam. Can't hurt power that's for sure. If the cam does not wake things up I can just get the head ported and I stall a HC piston.

  • Steel Panther

Posted October 19, 2010 - 09:39 AM


I dont have any problems keeping up with my buddy on his 07 kawi out in the desert on my 09 yz. We have dragged a few times and it just came down to whoever got better traction from the start. His kawi does make a whole lot more noise tho.

  • silvy423

Posted October 19, 2010 - 11:59 AM


Just don't ride your friends bike then, it will piss you off and make you feel like you own a 250f

  • motox100

Posted October 19, 2010 - 01:47 PM


I had an 07 and 08 YZ450...and the last couple years 09,10 I've rode the KX. An 08 YZ vs an 08 KX stock to stock was no contest...that muffler they had on the 08 YZ killed it. Once I put an aftermarket exhaust (Dubach) on the YZ it made a night and day difference. If it still is not enough for you some light head work, a little higher compression piston with the exhaust will really produce some gains.

  • silvy423

Posted October 19, 2010 - 05:07 PM


I really hope the piston and the 06 cam will help it out. As it stands now you should not have to work that hard on a 450! That shouldn't be that bad, $150 for a cam on eBay, another $300 for a HC piston. I hope to have a smile on my face with this bikes motor in the future. Thanks for the help guys, I'm just shocked at how slow it really is.

  • mywifefarts

Posted October 19, 2010 - 07:04 PM


I think you should cut your losses and by a Kawi.

  • silvy423

Posted October 19, 2010 - 09:56 PM


That's a great comment? Got the YZ new for $3200, so it's hard to let it go. I was simply hoping someone could chime in and say the bike has some balls with this combo?

  • tpars121

Posted October 20, 2010 - 04:09 AM


I agree with mywifefarts, whether your perception is real it is in your head now that the KX is faster and you'll think about it every time you ride.

  • erickdj

Posted October 20, 2010 - 06:30 AM


I agree with mywifefarts, whether your perception is real it is in your head now that the KX is faster and you'll think about it every time you ride.

Agreed. The bikes probably aren't that far from each other in the power department, they just differ in the way it's delivered. At this point it's engraved in your mind that the kx is that much more powerful/faster than your yz and you'll always have that in the back of your head, always second guessing yourself as to whether or not the yz is delivering the goods. I happen to own an 08 yz450f, it has a DrD exhaust and an 06 CDI, along with a 51 tooth rear sprocket. That bike is not hurting for power, it has more power than it needs and it's delivered in a very nice linear way. If anything, there's a constant battle for traction given all that power. Any more power and traction would be nearly at zero, which is not very conductive to fast lap times.

  • motox100

Posted October 20, 2010 - 06:35 AM


That's a great comment? Got the YZ new for $3200, so it's hard to let it go. I was simply hoping someone could chime in and say the bike has some balls with this combo?

The bike has some balls with this combo.

IMO...the Yamaha has plenty of power with just an aftermarket exhaust... more then most people can use on a track. With the stock silencer no doubt it's a dog. It makes different power than the KX (which feels more like a tractor)...the YZ motor is much smoother. I have rode a 09 YZ450 with an exhaust, some very mild head work and a HP CP piston. It motored.

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