04 YZ450F cold start

11 replies to this topic
  • mxdirtking

Posted February 27, 2010 - 06:25 PM


I recently bought this bike and it is the worst thing ever to get started in the cold. After about 5-7 kicks with the choke on it will backfire and then after about 3 kicks after the backfire it will start. I need some help on this one. Thank you

  • tek_01

Posted February 28, 2010 - 02:45 PM


You are going to need to check a few things first and also specify what cold means, how cold are we talking?

check what size jets you have in there to get a baseline. if the pilot is way off for your weather/alt than its going to be hard to start.

What helps mine (and alot of others) is to give the throttle 2 or 3 twists before you start kicking but dont touch the throttle after that.

  • mxdirtking

Posted February 28, 2010 - 08:29 PM


Its like about in the 30's. I checked the main jet and its the stock 165 and its got a pipe on it so im going to have to jet it so i don't know if that has anything to do with it and i'll try that 2 or 3 twists if it helps but right now i got it all torn apart and waiting for parts because the water pump went bad in it.

  • tek_01

Posted March 01, 2010 - 01:22 AM


I would think the idle circuit would be more of the problem , main jet doesn't kick in until about half throttle, what size was your pilot?
At a guess i would say it should be about 45-48 for that temp and altitude.

It never gets that cold where i live so im not too sure, but alot of others says they need 3-4 twists in extreme cold weather.

Also are the valve clearances in spec?

  • mxdirtking

Posted March 01, 2010 - 11:13 AM


Im guessing that it has the stock pilot jet in it. When i change the main jet do i have to change the pilot jet too?

  • tek_01

Posted March 01, 2010 - 12:35 PM


Nothing says you have to change them both

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  • kain522

Posted March 01, 2010 - 07:17 PM


Cold start on my 04 goes like this- 2 full squirts on the accel pump, full choke, and it will almost always start on the first or second kick. Even after a Wisconsin winter, it will fire in 5-7 kicks. Hope this helps.

  • mxdirtking

Posted March 01, 2010 - 08:40 PM


Nice! Its better info when someone knows the Wisconsin winters!

  • kain522

Posted March 02, 2010 - 10:41 AM


Did it work for you? Where in Wis are you? I'm in Waterford.

  • mxdirtking

Posted March 02, 2010 - 11:30 AM


My bike is all torn apart right now because that water pump went out in it but ill try it as soon as i get it put all back togather. I'm in Richland Center half way between LaCrosse and Madison>

  • kain522

Posted March 02, 2010 - 04:31 PM


Ok, my in laws are in Mineral Point. Maybe I'll see you on the trails this summer.

  • mxdirtking

Posted March 02, 2010 - 07:58 PM


You never know

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