1980 Z28 part-3 Why does my vacuum gauge go crazy like this. Whats your thoughts???


Veteran Member
Dec 7, 2014
Great suggestions here. There is some lifter noise going on, I'd check rocker arm adjustment, but do a compression check first to see if you can narrow down the cylinder that is the issue.
As Twisted said, I'd guess a valve is not sealing.
A plugged cat usually shows up worse under load, as in no acceleration.
Your initial timing is a bit low, even for stock, but that's not the vacuum issue.