Header turning blue/purplish....PLEASE HELP

4 replies to this topic
  • slammmin72

Posted October 09, 2006 - 03:07 PM


so i installed my JD jetting kit this weekend and took it to hollister to test it out. after riding if for a little while, i noticed that the header started turning blueish purple right next to the block. and also it pops when u are in gear going down hill with no gas....it runs great, tons of power (wheelies in 4th gear very easily) in intalled the jetting kit just like the instrutions said. blue tiped needle wiht the clip on the 4th positsion form the top, and the 170 jet in the bottom of the fuel bowl. i was a little woried that it was runnign to lean that moved the clip down one notch to ritchen it up some..not sure if that it the proper prcesure. this is the first bike ive had to jet. some one please help! thanks

btw, its an 02' YZ426F

  • Fastest1

Posted October 09, 2006 - 03:18 PM


Sounds like you have a titanium head pipe. Regarding the popping under deceleration, this is an indicator of a lean condition in the pilot circuit. The remedy is to turn out the fuel screw in quarter turn increments after the bike is warm til the pop is gone or very close to it. If you have to go more than 2 and 1/2 turns you will need to go the next size up pilot jet. I would return the clip to its position prior. The clip on the needle really controls 1/4-3/4 throttle applications the most. Regarding lean on 4 strokes, it is not nearly as critical since lubricants are not part of the fuel mixture. It still needs to be refined but shouldnt cause any problems as long as jetting is close. And if you are running JD's kit as he recommends, you are very close if not spot on.

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  • slammmin72

Posted October 09, 2006 - 03:41 PM


thanks, im gonna pull the carb apart tonight and put it back to its settings...if only i had a track in my back yard. as far as it being a titanium head pipe..im not sure...i bought the bike used, and its what it came with...i though it was the stock one..... and for the pilot jet..is that the 6mm one on the bottom of the carb in the fuel bowl?..sry, this is all still new to me..im used to my YZ250.where i just put gas in it and change the oil...thanks again..this might help aswell...


(yes i know there is a dent in the header....)

  • grayracer513

Posted October 09, 2006 - 03:56 PM


Mine is blue or yellow or purple all the way to the can. Normal Ti pipe behavior.

A little decel crackling on a YZF is a sign of having the idle fuel mix set right. If it pops loud and hard, it's either lean at idle, or there air in the exhaust system.

  • slammmin72

Posted October 09, 2006 - 04:15 PM


ok..so now im confused...i took the FMF Q series pipe off, and put my WB E-series back on (removed all the plates except for 5 so it meets the dB test) and took if for a quick spin on the street....no poping at all (except for the normal quiet poping that im used to)...whats the deal? ( i did find the pilot screw turned almost all the way in from yesterdays "tuning by ear"...(user error) so i backed it back out to 1 1/4 turns like JD says....i guess ill have to go riding again... :devil:

i guess the reason im conerned it beacuse ive ridden it plenty of times before..and hte header has always stayed gold....and hten as soon as i put this JD kit in, it turned blue/purple immedeatly...

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