Compression test??

It sounds like the exhaust valve seats are beat out because of unleaded gas. I had a '69 273 do the exact thing yours has done. It ran great after a valve job and intake/carb package them about a year later I noticed that it didn't run like it used to so I did a compression test and it was all over the board and low like yours. I pulled the heads and found the exhaust valves buried into the heads. I replaced them with '75 318 heads and my compression was 125psi.


Chuck