Whitelightnin',
Not sure why the insulator is there, but it goes back to the first downdraft carbs in 1932.
Probably to prevent percolation and vapor lock.
I'd say that if your vehicle came so-equipped, leave it that way.
I think it also has to do with the heavier trucks that used a governor in place of the spacer; that way the manifolds are made with one legnth of stud: no governor- use spacer; governor- no spacer, same studs.
My 250s w/ Rochester "B"s don't use the insulator.
Other ideas?
