Keith Hardy's wonderful site has a Rochester 'B' rebuild and troubleshooting guide. They merely call the holes 'vacuum ports'.
I have never understood why this seemingly important connection wasn't gasketed. The book shows no gaskets. I have used gaskets on both sides of the spacer before...maybe this wasn't necessary.
In the Rochester book I mentioned, if a leaking power piston is suspected which would result in a rough, rich idle, they instruct you to pull the carburetor and flip the phenolic spacer over, thus covering the vacuum ports to the power piston and taking it out of the equation.
They tell you that if the idle 'smoothens' out, you have found your problem! I didn't know 'smoothens' was a word. Google spell-check doesn't know about 'smoothens' but it does know about 'smoothies'.
Stuart
