Glowing head pipe

6 replies to this topic
  • Diesel0889

Posted July 18, 2015 - 05:08 PM


Hey guys so I just picked up a 2004 yz450f for a fun project. It was running a little rough when I got it it didn't want to idle. I played with the fuel screw and now it fires right up in 3 or less kick almost always. Well I did a oil and filter change today and let it idle for about a min time and don't think any more than a min and ten seconds and the head pipe was give or take about have way red. I had a crf supermoto and can't remember it doing this. I have read this is normal 4t don't like to idle long bla bla. I'm only posting to reassure myself this is normal and was hoping a few 450f experts would chime in and set me straight on the subject so I can better understand it as I don't want to wreck nothing if there is a underlying problem also. This bike is fast as he'll and I hope to make it a fun project for me to enjoy not need to save for major parts before I make it mine as for the moment it looks like a hunk of shit with the original plastics rear tire and ugly as he'll graphics lol. I want to make it mine then do a full rebuild after a few rides lol. Sorry for the rant. Thanks in advance.... Ben ps only mod that I see is a fmf head pipe with stock muffler...

  • 15thumper

Posted July 18, 2015 - 05:56 PM


Richen up the pilot jet

  • Jeremy250f

Posted July 18, 2015 - 06:00 PM


Put it back to stock jetting, the pilot or the fuel jet could be off

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  • Krannie McKranface

Posted July 18, 2015 - 06:14 PM


Bottom line:


If you have correctly chosen your pilot jet (using the method at the top of the jetting forum, or in countless threads in other forums), you do NOT modify the pilot jet size because of a glowing header.


That, and if you have NO deceleration back-fire/popping, your pilot jet size is already correct.


You fine tune the pilot circuit with the fuel screw ( you need and R&D fuel screw so you can do this as needed, regularly), and the highest idle acheivable by turning the fuel screw should equal approx 1.5 turns out from full (softly) in.  If it takes more turns to acheive highest idle, you pilot is too small. Less turns, and it's too big. That's it.


Then fine tune the speed of the idle drop after blipping the throttle, in 1/8 turns, the speed at which the idle drops. You want it to drop as fast as possible.


Your header is thin, and made of Ti, and gets hot very fast.  A track bike is not supposed to sit motionless, and the operating temp of the motor will go up 50 degrees compared to moving at 5mph, very quickly.

  • 15thumper

Posted July 18, 2015 - 07:49 PM


Richen the pilot jet

  • 03yzf450-kuke

Posted July 19, 2015 - 04:26 AM


Richen the pilot jet

as krannie said, glowing head pipe does not necessarily mean your pilot circuit needs to be richened. Header glow is normal when there's no air moving past it.

  • grayracer513

Posted July 19, 2015 - 06:27 AM


... if you have NO deceleration back-fire/popping, your pilot jet size is ...


Too big.  A YZ450 should pop "some" on decel when jetted right.  Not every time, not a lot, just "some".


High idle speeds, and in fact, an excessively rich mixture, can contribute to this, but if the bike still has a titanium header, it's entirely normal for it to glow bright enough to appear red in lower light levels, like  a shaded garage within 90 seconds. At that point, the header is about 850 degrees.

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