I hate karts as well. After reading this thread a week ago I tackled the karting events of International A and B. I finished A this weekend. I set the driver to "Push the pace" though I am not sure that is necessary. I don't worry about braking. I just tell him to accelerate most of the time, backing off into the turns. So, I am either holding R1 and X or releasing them. Sometimes I may give him a left or right nudge with R1 and the D-pad but I never felt that was terribly effective. The trick for me was running the race once or twice to get a feel for the rhythm of the race, knowing when to back off into turns and when to accelerate to cut inside a cart and move up a position. I am not great at these games so if I can do it, so can you. Don't let it get in your head. Know that B-spec can win the kart races. When it finally clicks for you you'll wonder why it seemed so daunting at first.
Now if only I could win the NASCAR event at the speed ring. I came in second once, right on the bumper of the 1st place car, but usually I am somewhere between 4th and 6th. I have 572 stars out of 573. The more frustrating it becomes the more likely I will accept my limitations and stop chasing my Moby Dick. :-)
Good luck with the karting. Don't give up!