2008 YZ450F Cold Starting Nightmare?

11 replies to this topic
  • Boise93

Posted March 08, 2008 - 06:34 PM


I just brought home my new from dealer 2008 YZ450F last night. This morning I went to start it when it was cold (40 degrees F.) and must've kicked the thing 30-40 times before it fired up with numerous exhaust pops before firing. This was with 91 octane, fuel on, choke out and stock jetting. I followed the directions in the manual to the letter, but this can't be right. The bike has 0.8 hours on it now from the heat cycles I put on it today. When the bike is warm, it starts on the first kick. My 2002 YZ250F never had this problem. Any ideas or tricks to starting this new machine?

Tell me what I need to do to cold start on the first or second kick as I can't stand my wife's "told you not to buy it", smirk.

  • harwood39

Posted March 08, 2008 - 06:48 PM


i have the same problem with my 426, well not when its as warm as 40, but after drivin 4.5 hours in -12 degree weather... takes about 30 min worth of kicking after i warm the pig up with a heat gun, but after that shes fine... they are just cold blooded and like heat...

  • maddogyz250f

Posted March 08, 2008 - 07:07 PM


My 06 is very sensitive to fuel screw adjustment when cold starting. If the beast will not start, I will lean the fuel screw and try another 5 kicks. If this does not work, I richen it and try again. It usually starts one way or the other. In rare instances, I have to turn off the choke, kick it 5-7 times and then kick it again with the choke back on.

  • yzaddict106

Posted March 08, 2008 - 07:12 PM


I had the same problem. Bump up your main jet. I believe stock is 160? throw a 165 in there and you should be good to go!

  • Justin89

Posted March 08, 2008 - 07:17 PM


I bought my 06' brand new also and it was the same way. Get a zip tye fuel screw...that wil help!

  • rickallen124

Posted March 08, 2008 - 07:35 PM


When it's fairly cold give it one or two blips of the throttle pull the choke and start it. Start with one blip and if thats not enough give it another. This primes the cylinder for firing and works really well to get it started the first time. You probably also need to go up to a 45 pilot jet and 165 mainjet if you are riding in 40 degree weather. That's what I went to for winter and now I'm going back to stock. A fuel screw does help fine tune the jetting.

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  • jesmer460

Posted June 10, 2008 - 04:48 AM


You have probably solved your problem by now, but it is really quite simple.
1st, make sure your fuel screw is set correctly. If it is less than 1.5 turns out the bike will not start consistently.
2nd, below 50 degrees change the pilot jet to a 48
3rd, use the tried and true 4 stroke starting technique. Warm weather turn the gas on, choke on, blip the throttle 3 time, push the kick starter through the cycle slow(you are not trying to start it yet, you are priming the cyclinder) 3 times. Now give the kick starter a regular starting kick. Also remember that the 450 does not like fast hard kicks like the 250 does. Just a nice easy steady kick. Mine always starts on the first kick after this procedure. When the weather is freezing the only change is 5 blips on the throttle.

Let me know how you fare.

  • todds924

Posted June 14, 2008 - 01:51 PM


I had the same problem. Bump up your main jet. I believe stock is 160? throw a 165 in there and you should be good to go!

Main jet has absolutely nothing to do with how a bike starts.

  • grayracer513

Posted June 14, 2008 - 03:57 PM


Main jet has absolutely nothing to do with how a bike starts.

Amen to that.

  • SF701

Posted June 14, 2008 - 06:58 PM


Turn the gas on, pull the choke out, turn the throttle to the stop and let go twice, then kick it. Do not turn the throttle while you kick it and do not use this method after you've started it for that day. Also, while warming it up, keep it at a steady rpm.

  • Pappy141

Posted June 15, 2008 - 05:56 AM


I have an 08 too...It responds great when cold with the 2-3 blips of the throttle. 1st or 2nd kick everytime.

  • corndog67

Posted June 16, 2008 - 08:04 PM


Two turns on the throttle, choke on, one kick, boom, fires right up, every time, even after a crash. Oh yeah, hot, no choke, and I usually don't use the hot start lever either.

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