Pour sugar into heavy-bottom pot. Stir in Karo syrup, water and evaporated milk. Let come to boil over medium heat; stir in salt.
After boiling a while, stir in pecan halves and lower heat a little. Stir constantly, till candy reaches soft-ball stage (234 degrees F). Remove from heat.
While candy is resting, set out waxed paper. When candy has cooled enough not to melt the wax off the paper, stir in margarine and drop