I have a 350 with a Holley 650 on it and it runs pretty rich. Is it true that when the air/fuel mixture screws are all the way tightened/in that the mixutre should be lean? What all comes into play in able to get a lean mixture?

If you're still running rich with the idle mixture screws turned all the way in, the screws are not your problem. Possible causes are the fuel pressure(too high), or the float levels(too high). Check your fuel pressure and float levels. Once you have found the problem and corrected it, set the idle mixture screws 2 1/2 turns out and tune from there.

Ditto. Something's wrong on the inside.

You do understand that those mixture screws are for the idle only...

Thanks guys