I've got a 2006 YFZ 450.
*Pro flow with k&n
*k&n air box lid
*full yosh exhaust
*gytr jet kit
*tusk fuel mixture screw.
I am riding at 3500 ft where should I start the jetting? Any help would be great. Thanks.

 

Your mods are in the common range. Put a call in to Yosh, they should be able to suggest something close to ideal. Run some plug chops etc. and fine tune from there.

 

Go to your dealer and get genuin kelihn jets. No jet kit! I'd start with a 165 and 170. The weather is changing so you might even have to go a little smaller.

 

The jet kit is OK. I just buy the Keihein jets that I need though. I'm running a 170 main but don't have an intake. I am at 500ft. BTW, you need to jet bigger in the winter, as colder air is denser and has more oxygen, therefor you need more fuel. But then again, you are a fair bit higher in elevation than I am.

 

The jets are keihin jets in the gytr kit. I understand jetting and have done it many times. I bougth the dynojet kit it was crap. The quad ran good but it sputtered on the top end. I know that it was rich on the main jet but I went from from the 165 dynojet down to 140 one at a time. It was 8 jets in all. It happened in first second and thrid but not in forth and fifth after dropping a few jets. I tried dropping the needle it still sputted in the first 3 gears on top end. I put in a 165 keihin still sputtered. I tried going back to the factory needle riseing it up from 3 to 4 slot it would make it richer I know but with the mods I figured it should be about rigth.I am going jetting tomorrow I hope I can get some where close to start. I do not think it was the rev limitter it has a tack and reved a couple of grand higher in fourth and fifth. Thanks.

 

All kinds of jetting info here check it out.

http://www.allthingsmoto.com/forums/...a399ff&t=12299

 

Heres even a better link with more info on jetting for altitude.
http://www.thumperfaq.com/jetting.htm

Hope this helps!