Sounds like your valve adjustment may be off. How did you adjust your " lash"? Since you have stock rockers, pushrods and valves, all you need do it run the rocker nut down and torque to 20lbs. Hot, cold, running or not, doesn't matter You're done! No gap, no lash. If the nuts are old they may not have the locking power they once did and might have a tendency to back off. Think about replacing them.