My son had similar problem. I had adjusted everything before he drove and everything measureed within tolerance. When he came in it was smoking. I checked everything again and everything measured within tolerance. Thinking he was riding the brake a bit I put some more freeplay in the pedal. Thus if he set his foot on the pedal it did not even start to move the pads until it went in about 1 inch. He came back in the next session with no problem.
I found out after the fact that he had actually spun out a couple of times in the first session because the brakes were too responsive. (The track he was at has a large portion that is not visible from the stands.) the brake adjustment helped his driving, and he was not burning the pads.