Valve adjustment question

[kxnomore]

I have been having some noisy lifters lately, so I decided today to try to tighten up the valvetrain, possibly for the first time ever based on the amount of effort to get the last traces of what used to be a cork gasket off the engine and valve cover.

But as I loosen the rockers up until they clack, and then tighten them until the clacking just stops, here is where my question begins.

How much further??? I was told 3/4 of a turn, but right at about a half turn, the engine noticibly changes pitch and kind of bogs down. Should I stop short of that happening and just go about a 1/4 turn??? or let the engine bog down a bit, and hope it recovers eventually???

Thanks in advance to any opinions or suggestions!