timing issues.

[j.rigby15r]

So here is my second thread this hour. I'm finally getting around to checking and setting my timing. I've got less than fifty miles on my rebuilt motor. It has a mild cam, edelbrock carb and intake, and gm hei dizzy that has been rebuilt and a mr gasket advance kit. The motor was running like crap but hadn't put a light on her since I was trying to put out other issues first. When I put the light on it was about 12° btdc which is were I wanted it. When I revved it up it wasn't really advancing. So I changed the springs to a lighter set and she started advancing but only to about 25°. I've tried adjusting it and when I get it to break 30° the idol timing is around 20°. It's running better but not quite were it should, I think. Also in another post I was reading about timing and a sluggish motor someone mentioned valve being too tight. How do I know if my valve lash was set to tight?