Jetting

FCR Jetting

The FCR carburator is differant from the old carbs. in many ways. When
jetting the FCR for a YFZ450 you must first decide several things.

1. Cam mod?? With the YZ cam or with the cam mod. the YFZ has
much more cam over lap and as such is better ridden wide open or on the
brakes. Part throtle riding like XC racing in the woods is better with the
stock cam setup. The extra over lap when the YZ cam is used will require
differant jetting.

2. Air box lid?? Jetting needs are completly differant with the air box lid
vs. with out.

3. What needle are you going to use?? This carb is controlled at all throtle
settings by the needle and extra fuel is added at closed throtle and at wide
open throtle by the pilot jet and the main jet.


Please do not call me with jetting questions.

I will try to post as much info here regarding the jetting that I am running
and how it effects the way that the bike runs.

I have tested the famous James Dean needle and jetting setup. With the
air box lid off, and the YZ cam it had great throtle response but ran
poorly under part throtle-no load conditions. This is very ridable and does
not effect how the engine runns in any way but the sound is very annoying.
This setup is the best I have tested to date for MX or dune type riding. I
ran it on the dyno to check the fuel ratios at all throtle settings as this is the
best I have ridden to date and I will use it as a base line for future testing
untill I have better. For info on this setup, go to www.thumpertalk.com.