Jetting 2009 YFZ450X for higher altitudes?

[4D.Adrenaline]

I'm new to this forum and I joined to look for some advice on jetting my 2009 YFZ450X for higher altitudes, around 5,000 ft. I recently got a big bore kit, DG exhaust, and K&N filter with no airbox lid. What would be the recommended size for the main jet and pilot jet? I'd appreciate getting your insights and suggestions!

 

[yamahahaha24']

I ride mine up in Colorado around 5000 ft with a similar setup and had good luck running a 162 main and 45 pilot with the needle on the 3rd clip. You might need to fine tune depending on temps and throttle response, but that should get you in the ballpark. What jetting are you running now and how's it behaving off idle or under load?

 

[Veronica.sims002]

You should lean it out a bit compared to sea level, start with a main jet around 160 to 165 and a pilot jet around 45, then be dropping the needle clip position, one notch can help with midrange

 

[brenty2444]

Nice setup! I agree with @Veronica.sims002 about leaning it out a bit. Have you noticed any bogging or popping on decel yet? That can help dial it in further

 

[Thelittlefriend]

A friend of mine is running 175 for main and 52 for pilot and says that it's running great. It's running a lot leaner, so keep that in mind as well. If you notice it bogging down, you may want a 40 leak jet just in case.

 

[RaptorChaser]

When I moved to the mountains with my YFZ (that I've tweaked a bit), I had some trouble at first. It kept running too rich and bogging down. I had to change the jets three times before I found the right setup: a 162/45 combo. That smoothed everything out. The altitude makes a big difference, but once you get it right, it really flies

 

[Dylan1]

At 5,000 ft with a big bore, DG exhaust, and open airbox, most riders lean down the main jet about 2–3 sizes and slightly richer on the pilot jet, but exact numbers depend on conditions