Number of Posts?

I’ve read a few of the support topics on this, but I still can’t get it right.
In Options > Reading I have Show at Most posts = 8
But no matter what number I change that to, I still only get 3 posts on the main page, before the Previous Entries loop starts up.
I’m guessing there’s something in my theme that’s over riding the options I set.
Where should I look to change the code so that I get 8 posts on the main page before the loop starts? Thanks!