Only have light Karo syrup for a pecan pie, but prefer dark--will subbing part molasses do the trick?
Dark corn syrup is light corn syrup plus molasses and artificial coloring. So, yes, you can substitute.
How about using some dark brown sugar instead of the other sugar in the recipe.
Subbing a significant amount of molasses (more than a tablespoon) will give it a strong flavor that will interfere, in my opinion, with the pecan. I agree with cheater chef, that you should sub some dark brown sugar. If you don't have brown sugar, use just a teaspoon or two at most of molasses. ;o)
I agree with cheater. My fave pecan pie uses only brown sugar. I find the syrup flavor off-putting by comparison.
i don't mind using molasses -treacle works just as well also. if you've not tried bourbon peacan pie- it's an awesome take on the traditional recipe.