where ever you heard not to use a timing light...umm don't listen to that source again. I don't know what you're talking about on the carb. You said somebody adjusted a screw on it...that doesn't mean much, there are quite a few screws. Idle speed screw? Idle mixture screws? If its the idle speed screw, just back off on it until your back down to about 700 rpms. For the timing, connect the +/- leads to their respective sources, then hook the spark lead to the #1 plug (cylinder at front passenger side). Disconnect vacuum hose from vacuum advance housing and temporarily plug the hose(a small screw works well). Locate timing pointer on timing cover, be sure timing marks on balancer are visible/readable. Make sure the leads for the timing light are not at risk of being caught by the fan or alternator, etc. Fire the engine, point timing light at pointer/balancer. The light will flash everytime the #1 cylinder fires. Your initial timing at idle should be approx 12* BTDC. To adjust the timing, grab a 1/2" wrench and loosen the bolt that secures the distributor hold down clamp. Rotate the distributor slightly clockwise to advance the timing, counterclockwise to retard the timing.
I don't know how else to explain it. It should be clearly explained in your manual (if you've read it). It can be set by using a vacuum gauge, but I think thats beyond your skill set at this point. Plus, if its a stock (according to your sig it is stock for all intents and purposes) engine the factory procedure should be just fine. I could go into adjusting the advance curve, idle mixture adjustment, etc, but I think that would blow your mind at this point.
For info on the carter carb, go to their website. Or shoot, go to edelbrocks website, they are the same carb. They should both have a basic trouble shooting guide on their website.