That's an aftermarket mikuni. It's pretty close to a stock zilla carb.
TM flatslide 38mm

I have the exact same carb on my 250
There's some info for you here, look at the TM38-86, that'll give you all the specs.

http://www.mikunipower.com/TM01.htm

I converted my thumb throttle to a motion pro twist throttle. I found an adjustable cable that worked with my setup.
Motion pro has adjustable cables you can buy. This is the one I have that has a middle adjustment to dial in for my setup.
http://www.motionpro.com/motorcycle/partno/01-0222