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

[QUAKE_WARS]

I have new carb. New wires, cap rotor, coil, spark plugs. For now I have the timing 6 BTDC. No slop on timing chain. All vacuum ports blocked off. I fixed timing today and its starts on it's own now
but still very shaky. This is kicking my ass!! Whats your thoughts?

 

[Twisted_Metal]

That type of behavior is usually valve related.
It could be as simple as improper rocker arm adjustment or a broken valve spring.

 

[QUAKE_WARS]

I can hear one lifter tap on driver side. not to bad

 

[Twisted_Metal]

Do you have a compression tester?

Check all cylinders and report the results.

 

[QUAKE_WARS]

ALREADY ON AMAZON BUYING ONE.

 

[QUAKE_WARS]

Also forgot to say it has original catalytic converter. Is there a way to test if this is clogged?

 

[FNFAL308]

2 plug wires wrong?

 

[xten]

Try spraying carb cleaner around the carb (base) and intake manifold for leaks. If idle goes up, you found the problem.

 

[rocket dawg]

https://www.onallcylinders.com/wp-content/uploads/2016/03/31/vacumm-reading-1.png

 

[biker]

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.