Start with Walt's "dime" air gap on the firewall adjuster. I.E. with NOTHING on and/or running, grab ahold of the cable, and you should be able to pull it out of the firewall adjuster the width of a dime.
Now, if that is where you are, and it STILL won't go into second, ya need more "throw" on that cable. So what you have to do is run the firewall adjuster OUT a few threads more, and try it again.
Is the cable itself adjustable? Is the clutch plate new/used? Is the cable new/used?
NOT knowing the answers to the questions I just asked, and ASSUMING (we all know what assuming does!!!!) all the parts are new, and we have an adjustable cable, AND firewall adjuster, here's what I would do:
Run the firewall adjuster all the way IN. Yes, IN. Towards the firewall.
Get UNDER the car, adjust the cable so that there is MINIMAL "play" in her. For a stock clutch 1/8" throwout air gap is MORE than enough!
Back up on top, start with Walt's "dime" theory on the firewall adjuster, and then TRY IT.
If it still won't shift, ya need more throw, like I said. So run the firewall adjuster OUT, no more than 1 full turn at a time. A "little" really is ALOT here!!!!!
Keep playin with it, and you WILL get it. Trust me!!!