I have the same problem with my 83 ZXT. I was told that it needs new hydraulic rocker arms.... You are looking at about 30-80 dollars each with 12 total to do the job right....
If this fixes your problem let me know because I am in the process of ordering parts for a complete re-build on mine...
If this fixes your problem let me know because I am in the process of ordering parts for a complete re-build on mine...