Please clarify what you mean by ".... I can not get it to idle below 1000 as we are bottomed out on the idle adjustment ..."

Does this mean that the throttle plates are open as far as possible with the adjustment screw at 1000 rpm, or are they in the closed position?

When at an idle in neutral, if you put you hand over he middle carb to choke it, does the idle speed increase initially before dropping off?....if so, it could be a vacuum leak.