I dont know if this will help but it might, I got the pro curcuit t-4, K&N filter, and i drilled holes in the airbox lid, i put duct tape over the holes and remove and add it to better tune for humidity,temp and altitude. I am at about 500-600 feet, i am running a 150 Main, Stock pilot, And my needle three down from the top, If i take the needle clip up another notch it gets rid of the small off idle stumble i have, it actually makes it very very snappy, but it makes it a biotch to start, i dont notice my stuble because i always give it a little gas to get it going,

I know why mine stumbles and it may be the cause for you, my accelorator pump sticks just a little, every once in awhile but as long as u keep it a little above idle i dont notice it, I just thought i would throw that at you so you could check that.

Ryan

 

What can I say, jetting can be a slow, painfull thing. I would also lean the needle to the next clip.
I would like to mention one more thing for the folks that can't get rid of the stumble.... Take a look at your needle jet, AKA emulsion tube. I had a friends bike drive me nuts with a 1/4 throttle stuble we could not get rid off. His bike had a few years and a lot of miles on it. We found that the needle had worn the needle jet oval. The mix was dribbly insted of a nice mist like spray.