Jetting a yfz450

[Yamahacatfish]

I just recently rejetted my YFZ450 in my garage. I followed all the instructions. Checked, double checked and rechecked ALL my work... It just doesn’t run right in the upper RPM range. The only mods I have on my quad are I have a Looney tuned dual exhaust, and a ATV pro power pack (k&n filter, billet bracket and all that jazz, dynojet jet kit). I put the supplied pilot jet in (there was only 1), I threw in the #165 MJ (I left the air box lid off). I took the new needle and put the clip on the 5 groove from the top. I did everything just like it said.. Well when I started it up in the garage it sounded great. The next day I took it out at about 3k feet in elevation. It ran like crap.. When I took it into the upper rpm range it started sputtering or missing (cutting in and out). I took it home and put a #144 MJ in and it still ran like crap even with the air box lid on.. Do you have any suggestions or anything to get my quad back on the road?

[dudleydoright15]

What elevation are you at?
I am at 200ft elevation in central CA.

175 main
45 pilot
YZ 450 F needle out of dirt bike carb $14
2 turns out fuel air screw

W-E2 header and pipe, pro flow intake .
airbox lid off

[Yamahacatfish]

I'm at about 100ft above sea level so that should work great for me.. Thanks

[jshtex]

I just noticed in your sig that you have a Dyno Jet jet kit. The Dyno Jet jets run larger than the Kehin jets that came in the carb. A 165 Kehin is actually quite a bit smaller than a 165 Dyno Jet so keep that in mind when you are asking for or getting jetting advice.

So... a 165 (Dyno Jet jet) might be too rich, and the 144 you switched to might be too lean.

We run Kehin jets and ours was tuned on a dyno with air fuel capabilities. Our runs best with a 162 MJ, a GYTR needle on the 4th clip position and a 45 pilot. Two of our friends quads with similar mods were also tuned on another dyno, one uses a 165mj and the other is at 168.