cam and crank timing????

I have heard people say to retard your cam timing. How should I do this when replacing the timing chain and gears?? I have heard people say that you get better low end power by doing this, is this true?? and how do I do it?? If you know of a web sight that give instruction of how to set up cam to crank timing please let me know. I would like to have some more low end power. Thank you all.

p.s. I am running a E-303 cam and I have no electronics, just air gap intake and 600 cfm carb on a 1990 roller engine.

Thank you all for your help

anyone???