Very low unless those are not in PSI.

Plugs 5&6 seem a little lean.

I know we have gone through the ignition system before but don't remember everything that was tried. An all new hotter ignition system might be worth a try before you dig into the motor

jalex should put the engine specifications in his signature.  Carbs, ignition system, etc.  Can't remember the details.

A multi-spark ignition system might help for something like this.  MSD.  Cheaper than an engine rebuild.

The low cylinder pressures could also be caused by an adapter on the gauge.  But those are very low, as stated.  I think that I used an adapter once and got 125 instead of 175.  80 psi is waaaaay low.  I thought the numbers were higher, in past posts.

If those numbers were found with a good gauge on anybody's factory stock engine you'd say that the engine was worn out and needed a rebuild.

I agree with Zed. Numbers are way low. Bad gauge, bad methodology or bad rings...

Updated signature would help the memory

Multispark would be interesting maybe Megajolt? Although tuning could be an issue...

I would want something as hot as I could get. Blow your fingers off hot! 😉

Does anyone agree a leak down test would plainly tell the issue here?

How about trying a retorque of the head bolts. Low in the front and rear is odd. I torque mine from the center out.

3 hours ago, Barefootdan said:

are those numbers dry or wet? hot or cold? throttle fully open? Seems low, but at least consistent

@jalexquijano This info may add another piece to the puzzle.

1 hour ago, Yarb said:

Does anyone agree a leak down test would plainly tell the issue here?

His problem seems to be oil-fouling of the #4 spark plug.  And maybe #6.  His pressure numbers don't show that #4 is different from any of the others.  #3 and #4 are 19% higher than #1, which is at 73 psi.  But #1 spark plug and cylinder work okay, apparently.  #1 plug actually looks very clean in his picture above.

Not sure that anything will become obvious anytime soon.  Cylinder #4 has the highest pressure of all, along with #3.

 

https://www.championautoparts.com/Technical/Tech-Tips/Common-Spark-Plug-Problems.html#:~:text=Oil fouling occurs when oil is allowed to enter the combustion chamber.&text=Oil deposits cover the spark,sign of advanced engine wear.

1 hour ago, Mark Maras said:

@jalexquijano This info may add another piece to the puzzle.

Compression test was done at the mechanic shop this morning, 20 mins drive from home. So engine was hot. It was a digital compression tester. I did change the plugs last night and replaced them with new ones. I can post pictures again if you like.

The test was done with new plugs.

37 minutes ago, jalexquijano said:

Compression test was done at the mechanic shop this morning, 20 mins drive from home. So engine was hot. It was a digital compression tester. I did change the plugs last night and replaced them with new ones. I can post pictures again if you like.

 Do you know if he held the throttle wide open during the tests?

1 hour ago, jalexquijano said:

The test was done with new plugs.

The test is best done with all of the plugs out so that you get good engine speed from the starter.  If you have a slow cranking speed you'll get lower numbers.