Top speed, the rev limiter and jetting


8 replies to this topic
  • Regalman

Posted April 13, 2009 - 09:37 AM

#1

I've got a couple of hundred miles on my 2008 WR450 so I decided to open it up this weekend. Its stock other than free mods. (OEM AIS kit, grey wire cut, and exhaust noodle removed)

It hit 88 mph on the stock speedo on flat road. It didn't seem to hit the rev limiter. Does that sounds about right? Were is the rev limiter with stock gearing in relation to MPH. I'm guessing I must have been close. [heck, I'm just assuming there is a limiter, never hit it in any gear.]

Is this normal or do I have the jetting off a touch?

How close is the speedo to being accurate?

  • William1

Posted April 13, 2009 - 10:25 AM

#2

Sounds low. You have about 45 Hp, should be about 95. Might want to do a main jet checking/adjusting

  • KennyMc

Posted April 13, 2009 - 10:27 AM

#3

Just to cover all bases, you do have the throttle stop removed, correct? I don't know what the top speed is with it in/out:excuseme:

  • Regalman

Posted April 13, 2009 - 10:37 AM

#4

Yes, I used the new stop that came in the AIS kit.

William, think I should maybe wedge the airbox open and see if I gain anything?

Riding in the woods the jetting seemed spectacular, it never bogs or anything coming off the bottom... but this is the first time I ever open it up and expored the top end.

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  • William1

Posted April 13, 2009 - 10:38 AM

#5

You know,,,,,, what oil are you running?


























Inside joke - Not another oil thread trolling!!!
Posted Image

  • Regalman

Posted April 13, 2009 - 10:43 AM

#6

Well duh...

Posted Image

:p

  • William1

Posted April 13, 2009 - 10:46 AM

#7

Yes, I used the new stop that came in the AIS kit.

William, think I should maybe wedge the airbox open and see if I gain anything?

Riding in the woods the jetting seemed spectacular, it never bogs or anything coming off the bottom... but this is the first time I ever open it up and expored the top end.


Did you remove the snorkle and the rectangluar plastic part? I assume you did.

Go up one size in main and retest. Keep going up until until speed drops off. If speed drops off the first time you go up, then you are rich and need to go down.

In a perfect world, there will be one main that gives you max top speed. Next larger or smaller slows you down. If you find there is a range of three jets that alll give you the same top speed, go with the middle one. If just two jets do it for you, then go with the richer of the two for cool weather and the leaner one in the heat of summer.

  • Regalman

Posted April 13, 2009 - 10:55 AM

#8

I gotta pull the carb to replace the main, correct?

  • William1

Posted April 13, 2009 - 11:23 AM

#9

Nope, super easy on a Yamaha. Fuel tap off. Gently open the drain screw on the bottom of the float bowl. Put a jar under the hoses near the swing arm, drain the carb bowl. Place a rag on the engine cases below the carb, remove the cap on the float bowl (17mm). Main jet is right there. Just be gentle.




 
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