What are the numbers stamped on the side of the carb?
One thing I learned early on was the 87 Mikuni Carb was prone to leaning out the motor on deacceleration (need further back up). Seems like the ZIlla crowd likes and uses the 88 and up Mikuni's
Now speaking from experience, I had my Mikuni worked over by Jerry Hall. It starts great, idles, and works well. I rode the sand dunes in 90 degree heat and just recently rode in chilly 50 degree fall weather with a minor adjustments.
On the old site there was
post after post and post about people having a hard time getting the idle circuit on the Keihins to run. This may also contribute to the legend of the hard starting Zilla. Just my 2