When the intake valve is open, adjust the exhaust to zero lash and then 3/4ths a turn more. 1/2 a turn if the cam is anything radical or if you've installed 1.6 rockers or both. Repeat on the intake when the exhaust valve is open. Repeat 8 times. If you are using solid lifters, use a feeler gauge in...

If the pop is constant, make sure the exhaust valve is opening. The rocker stud can pull out.