8 replies to this topic
  • BlueThunderWYA

Posted June 07, 2002 - 09:08 PM


(YZ400)My jetting is pretty much set up for Glamis (about sealevel), however when I bring it to higher elevations it likes to backfire upon deceleration. The bike seems to run absolutely fine, I'm just wondering if this may create problems in the future, or should I stick with the rule; If it aint broke, don't fix it. Plus it sounds pretty cool when it backfires.

I'm also running a Wiseco pistion, Power Core IV can with header pipe, and a Factory fuel accelerator. Would this set up have anything to contribute?

[ June 08, 2002: Message edited by: BlueThunderWYA ]

  • Boit

Posted June 07, 2002 - 09:25 PM


From my own personal experience in tuning this machine, and also paying attention to how the new breed of thumper flattrackers, a little muffled pop on decel seems to be desirable. I attended the Houston round of the half mile thumper series and noticed how the fastest machines popped a little going into the turns. My '00 sounds just like those guys and my throttle response is instantaneous.

  • Guest_mxrider426_*

Posted June 07, 2002 - 09:40 PM


When you say backfire, do you really mean a loud gun firing noise out of the intake, or just popping noises out of the exhaust (afterburn)? popping noises are normal, but it shouldnt backfire very often. Both are lean issues.

The altitude should make your bike richer, but if it is very much colder, it will make it lean. Try turning the fuel screw out. if it is very lean, you may need a smaller pilot jet.

  • Boit

Posted June 07, 2002 - 10:55 PM


mxrider426; I think you meant a larger pilot.

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  • neWRiver

Posted June 07, 2002 - 11:04 PM


I could be off here, but isn't excess fuel the cause of the popping in the exhaust? Sounds like it occurs when the jetting is becoming richer. Work the fuel screw in a little bit and see if that helps.

  • John_Lorenz

Posted June 08, 2002 - 04:33 AM


did you see the hayden bros racing the thumpys at illinois

Man they was sweeeeet

  • BlueThunderWYA

Posted June 08, 2002 - 08:36 AM


I guess I'm doin' good then. It just pops, nothing too violent, ocasionaly bang. Thanks! Yeah the Hayden bros have the life!!!

  • Guest_mxrider426_*

Posted June 08, 2002 - 02:36 PM


Sorry, I did mean larger.

  • Boit

Posted June 08, 2002 - 04:56 PM


Ego; No I didn't, but I heard it was outstanding.

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