Leaks were my thoughts as well but we had every vacuum entry or exit on the carburetor sealed or leading to it's "proper place" and sealed tight there. My only other guess is that there was a gap somewhere between the spacer and adapter or carburetor and spacer.
1967 Chevy truck "The Hurricane"
WARNING:
This suspect has a tendency to jerry-rig.
"My engine ain't fast, but I pulled a tree trunk out of the ground once."
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