overheating maybe qustion? air fuel setting?

5 replies to this topic
  • hookedonjuice

Posted June 09, 2005 - 02:27 PM


ok i have a98 YZ400F and just did the 03 cam mod, power paks dividers in the carb, new timing chain, FMF titanium 4 silencer and mid pipe (stock head pipe), and a hot cams intake cam. i ran it for about 20 minutes and noticed it was idling funny and losing some water out the over flow tube. it was idling kinda hight so i adjusted the idle a little and then it would die almost and then jump up high on idle and then back down. it surging for some odd reason. i am running stock jets in the entire carb. what is a good setting for the air fuel screw on this bike with these mods. do i need to rejet for the cam change? when i killed it i couldnt even come close to putting my hands near the motor. i have the air fuel screw set at about 1 3/4 turns out.

  • YZ250F_Rider

Posted June 09, 2005 - 03:25 PM


check the plug after a throttle chop. If it's white keep putting a bigger main jet in until it turns a tan color on the ceramic. then go back and readjust the idle and fuel screw. After you get them sorted out raise or lower the needle until you get a decent cruise at 1/4 to mid throttle without popping sounds, and a decent transition from closed throttle to wide open (not boggy).

definitely either run engine ice or amsoil coolant (there the same stuff) though. With the cam your going to raise the temps just from packing more in, the exhaust pipe will also add heat by causing it to run leaner until you rejet.

  • hookedonjuice

Posted June 10, 2005 - 05:17 PM


thanks for the advice i will se what i can do.

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  • sirthumpalot

Posted June 11, 2005 - 04:36 AM


If the problem is at idle then fiddle with the fuel screw and if needed the pilot jet. Sounds like you're a bit lean due to the surging idle. But before you fiddle with the settings, make sure you have no air leaks, your hot start isn't sticking and that the carb is spotless inside.

  • hookedonjuice

Posted June 11, 2005 - 05:26 PM


yea i think it is in the air fuel setting also, it sure acts like it.

  • jamieyz426f01

Posted May 16, 2006 - 09:24 AM


are you 100% sure your timing is correct?

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