Winter jetting 09 yz450f

Well it's time for some winter riding here in WI, if you don't know already i used to ride a Ltr450 with fuel injection and didn't have to change anything for winter riding other than thinner oil and some studs in the tires. Now that i riding this Yam, i know i'm going to need to jet for the colder temperatures. What would you guys recommend for temps ranging from -5 to 25 degrees F? I'm new to jetting carbs so please be specific. Thanks everyone

Assuming your bike is correctly jetted now, increasing the number size of the jet by 1% for each 10 degrees drop is a good starting point. For example, if you have a 165, and you usually ride in 80 degree weather, and you want the correct size for 10 degree weather, subtract 10 from 80 to get 70 degrees drop. That means a 7% larger jet, so 165 x 1.07 = 176. Round that to either a 175 or a 180. Do the same for the pilot.

I live in Illinois and our winters are basically just like yours....Ive rode winters all my life and have never rejetted at all...been ridingf 4 strokes since 93, same deal..no need to rejet. I currently ride a 2009 yz450 and i wont rejet it either. You will probably need to adjust your air screw because cold air contains more oxygen.....remember LEAN IS MEAN!!! you bike is gonna run awesome in the winter!!

I live in Illinois and our winters are basically just like yours....Ive rode winters all my life and have never rejetted at all...been ridingf 4 strokes since 93, same deal..no need to rejet. I currently ride a 2009 yz450 and i wont rejet it either. You will probably need to adjust your air screw because cold air contains more oxygen.....remember LEAN IS MEAN!!! you bike is gonna run awesome in the winter!!

Going from 90 degree temps to sub freezing temps without changing your jetting means you are not realizing the potential of your bike. The pilot screw cannot make up for that much temp difference, and that only changes the pilot circuit. And lean is sometimes mean, on your wallet!!

Understood, however i i'm not even sure about the location of the "Air Screw" (pilot screw) the only one i am familiar with is the one that adjust the idle.

Understood, however i i'm not even sure about the location of the "Air Screw" (pilot screw) the only one i am familiar with is the one that adjust the idle.

The pilot screw in located on the bottom of the carb (bowl area). I would recommend getting a longer aftermarket pilot screw so you can easily adjust it by hand.

Thank you, I'm never able to search out the correct information on this site for some reason.

Well, those four posts were in Common Threads, which is is subtitled "look here first". :busted:

Look in the board FAQ's for tips on advanced searches.

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