-5 Degree Jetting

6 replies to this topic
  • crfrookie

Posted January 17, 2008 - 08:49 PM


There is an ice race this weekend and with temperatures at or below 0 degrees I am thinking stock jetting on a yz450f is not going to cut it. Any suggestions or a ball park of what I will need to change for this kind of cold riding would be appreciated.

I believe stock settings for the 06 are as follows;
Main Jet #165
Pilot Jet #42
Jet Needle #? not sure
Leak Jet #55

Thanks for your time.

  • Vetmxrider

Posted January 17, 2008 - 09:40 PM


If that is the jetting you would run for 70 degrees at sea level (stock) then I would try a 45 pilot and a 178 main for sea level at -5 or, a 45 pilot and 175 main for 2000’ foot elevation at –5 degrees.

  • grayracer513

Posted January 18, 2008 - 07:02 AM


That sounds about right, although I think the pilot should be a 48. Reason is that the 42 is, in most cases, too lean at 70-80 degrees in the first place, and I run a 45/165 in both my '06's 95% of the time in California.

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  • bedell99

Posted January 18, 2008 - 04:36 PM


Make sure you changer your oil to a lower weight or 0W oil.


  • Yamahafan

Posted January 19, 2008 - 06:43 AM


Using the 15 degree rule for main jets (one step up for each 15 degrees cooler) produces 165 -168 - 170 - 172 - 175 - 178.

If you use the actual correction factor formula:

Correction Factor (CF) = 1.0778-.00111*T + (2.38554*10^-10)*E^2 - (1.0777*10^-5)*E
T is temperature in degrees F; E is elevation in feet

You get a 177 mainjet for -5 degrees @ 2000 feet elevation. I would bring a 180 mainjet as well for backup. I have seen it written here many times that 450s like gas when it is cold. Also, minus 5 is pushing the envelope. I think the correction formula may be calibrated for more normal temperatures.

I would also post your question in the jetting forum where you might get somebody who has more experience with extreme cold temperature racing.

Why are you punishing yourself this weekend? Couldn't get a ticket to the Packer game?:cool:

  • crfrookie

Posted January 22, 2008 - 08:16 PM


Even with the bitter cold temps this last weekend we had a really good showing of racers.....probably cause all the Packer tickets were sold out.....

Anyway I installed a 170 main jet and the bike ran fine at 1/2 throttle to full. It however was horrible from idle to half way. Lots of bog and idle was very inconsistent. I was unable to get the larger pilot jet in time for the race. Do you think that this was the reason for the poor responce from idle to half open? I played with the fuel mixture screw and it helped but not alot. Not sure on this one??

I also had a problem with my throttle sticking open. It would not want to rebound back and when it did it was really slow. I took the throttle tube off and made sure that there was no snow or moisture causing it to stick. Once back in the garage I dissconected the throttle cables and they work just fine. Could the problem lie within the carb slide or do you think the cold has something to do with it. Everything appears to be fine but thats inside a heated garage. What should I look for first?

  • grayracer513

Posted January 22, 2008 - 09:03 PM


If the idle is too lean, it can cause the engine not to idle down as it should.

The stumbling you mention up to half throttle is likely caused by the same issue. But another thing that can be done is to use a needle with a smaller diameter shank (the straight portion above the taper). Try an NFLP needle (5TA-14916-LP) with the clip in 4 or 5 to start with.

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