Big vacuum difference 3 cyl around 20, one just 9.

Good compression, I adjusted removed carbs, nothing changed. Checked manifolds, no leaks!

Does it improve when you adjust the carb sync screw to raise the slide? Also, have you checked the valve clearances? Ed

I adjusted valves, all exhaust clearances were low, I switched shims and only needed 1 shim.
Compression is about 140 in problem cylinder.
I found air screw very tight, less than 1/4 out, adjusted it to 1 1/4 like book says, but it didn't change anything.
I removed pod filter from another cylinder, it didn't change vacuum in that cylinder (clogged filter check)
The only crazy idea is that carburator has hole in it sucking extra air (???????????)

Did you adjust the carb sync screw to raise or lower the slide to see if that changed the vacuum level? The sync screw is not the air screw. Ed

I was trying to adjust it, it didn't work.
My last chance was cleaning "choke" system. I pulled out all plungers, cleaned everything, it didn't work.

car5car wrote: I was trying to adjust it, it didn't work.
.....

Sorry, I don't understand "it didn't work." Was there a problem with the locknut and/or the screw, or were you able to loosen the locknut and turn the screw but there was no change in vacuum? We are talking about the same screw, right? The one under the carb's top cap? Ed

650ed wrote:

car5car wrote: I was trying to adjust it, it didn't work.
.....

Sorry, I don't understand "it didn't work." Was there a problem with the locknut and/or the screw, or were you able to loosen the locknut and turn the screw but there was no change in vacuum? We are talking about the same screw, right? The one under the carb's top cap? Ed

I begun increasing vacuum in problem cylinder, it improved from 9 to 11, after that throttle valve touched bottom and begun rising 3 other valves, increasing idle.
Yes, screw under top cover.

Problem is solved!
I left vacuum port on 3rd carb open. (I thought, it was vent port, looks identical to vent ports on 2nd and 4th cyl.)