Tuning Zenith WIP Carburetors

For the life of me I can’t seem to tune these carbs and set the timing.

The situation:

1. NOS carbs I bought and since have put 2000 miles on them in 20 years
2. Rebuilt the carbs last summer. Soaked in carb cleaner, new gaskets.
3. New timing chain 2000 miles ago
4. New headers last summer. Replaced intake/exhaust gasket
5. Totally new fuel lines and clean gas tank (how many of you can say you used muriatic acid in a gas tank?)
6. Electric fuel pump and regulator positioned after mechanical fuel pump because crank lobe is worn
7. Pertronix ignition in a 45D distributor that has 2000 miles on it
8. Set to TDC by observing #1 piston

Car starts and idles, but surges, backfires occasionally. I’ve driven around town and it will run for hours. I have a vacuum gauge on the dash. See the readings in the video compared to the tach.

I must have a leaky intake. But I sprayed starting fluid and found no result.

I could have a blocked exhaust, but it could only be the muffler or resonator which are stainless steel and have about 2500 miles on them but are 25 years old.

I adjusted the valves to spec cold then hot.

The vacuum gauge tends to read 5 at idle, 15-18 at high RPM

My compression on cylinders 1) 114 2) 111 3) 112 4) 115. So low, but not too low to run.

I don’t know what to do. I keep adjusting and never get the result I want. I have followed the WSM, I have followed YouTube, I have followed advice from friends.