Why is my pecan pie always runny? My pecan pie used to be firm years ago.  Now going by the same recipe it's always runny.  This time I added an extra egg, stirred it less and with a wood spoon so as not to get air and foam in the mix.

The full recipe: stir 4 beaten eggs into 1 cup karo, add 2T flour, 1/2c white sugar, 1/2c dark brown sugar, stir, add a pinch of salt, 1t vanilla, 1 1/2c pecans, 2T butter, mix gently. Pour in a 9" unbaked pie shell and baked at 350 degrees for 45 to 50 minutes.

The only think I have changed from the way I used to make it getting a firm filling is using dark brown sugar instead of all white sugar. I have never cooked the filling before pouring into the pie shell.  I have tried adding more flour and it didn't help. How do I fix this?
I'm looking at the recipe from Karo. The only thing that stands out as potentially being your problem is that the Karo recipe calls for a longer bake time. That recipe gives a final temperature too, 200F (93C). Could it be that your pie is undercooked?