Winter yz jetting

Mx391
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Mid, TN US
Mx391
I've got a completely stock 18 yz250 with stock jetting. Starting to get a little chilly here in TN. What jets should I change to account for the lower temps?
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kb228
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1/31/2018
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Mansfield, OH US
kb228 11/8/2018 5:19am
11/8/2018 5:19am
what jets you need to change is entirely dependant on how far your throttle is open when you have issues.

That being said youll need richer jetting for colder weather. You might get away with adjusting your clip position and adjusting the air screw
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barnett468
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Wildomar, CA US
barnett468 11/8/2018 7:28am
11/8/2018 7:28am
In general, if the bike is properly jetted for one particular ambient temp, the main jet does not to be changed unless there is a difference of at least around 30 degrees in ambient temp providing there is not a significant change in the elevation it is being ridden at.
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pete24
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Marlborough, MA US
pete24 11/8/2018 7:44am
11/8/2018 7:44am
the last yz250 I had was a 16 so should be the same as yours, I ran stock jetting from 45 degrees to 90 degrees here in new England, straight race gas 32:1 with spectro sx premix
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Pirate421
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MA US
Pirate421 11/11/2018 3:29pm
11/11/2018 3:29pm
I rode today in NH and my jetting was really good. 0-1500ft
38* degrees F
Pilot 50
Needle N3EW 2nd clip
Main 180
Talisker
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Houston, TX US
Talisker 11/13/2018 12:51am
11/13/2018 12:51am
Run it then check it. Sometimes the cold weather (depending on how cold) will clean up the jetting and make it perfect.

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