fcr differences?

[panteramatt]

Are there any differences besides size between the 39,40,and 41mm fcr's? Is one easier to tune than the other?

[cals400ex]

the 39 and 41 are essentially the same thing, one is just bigger. i believe the 41 actually does taper down in to 39mm's though at the end so it can fit into our air boot on the head. the 40mm fcr is a newer carb. i have been told it outflows the other two on a flowbench. i have ran the 39 and 40. the 40 is tough to get to fit right on a 400ex. it hits the gas tank and you need to make adaptors to make it fit properly. all of them are similar and didn't find tuning one easier than another. i changed motor mods when i changed the carbs so i can't really tell you if one perfomed better. with both the 39 and 40, if i snap the throttle really quick at low rpms, the bike would hesitate.