I was reading the jetting forum about how to adjust the pilot circuit.  It mentioned 2 different adjustment ranges depending on whether you had an FCR carb or CV carb.  What does the 450x have?
Thanks,

buckboss1 said:

450x is an FCR carb.  40mm.

I'm wondering, what does fcr and cv stand for?

fcr is just a model designation I believe,  CV means constant velocity.  The main difference between them is on the fcr the throttle cable is physically connected to the slide. when you twist the throttle the slid raises opening it up.  On a cv the cable is attached to a butterfly valve (like a choke on a car carb), when you open the throttle the valave turns opening the carb throat, BUT the slide is attached to a rubber diaphragm and will only lift if there is enough diferential in pressure/vacume to lift it.  The idea is no matter what your right wrist does the slide will only open enough for what the motor can use, maintaining a constant velocity through the carb bore.

CV are usually used on street bikes and can fuel very precisely for emissions and have good run quality. The down side is throttle response due to the indirect connection between throttle and carb slide.

FCR,   better throttle response and they also use a accelerator pump, which supplys a shot of fuel when the throttle is wacked open. Fuel that the other jets cannot supply fast enough (creating a lean moment).    CV carb can also use accerator pumps but it's not too common on most bikes.