nah, no prob at all. I went for a company-only Kart race a few years back, and I spent the weekend before the race (t'was to be done on a monday - work day heheheh) driving around with GrandPrix 2 (remember that game?). Come race day, As soon as I had my butt in the kart, all the "turn wheel X to turn Y radius" went out the window and I qualified 3rd, having arrived late and missed the 30mins practice session and half the qualifying. Then on the race, I ended a very respectfull 2nd place, gaining around .3 seconds per lap to a guy that raced those karts in a championship, every week. (he came with his helmet, race suit, back harness, gloves, race shoes, the works. I was with a t-shirt and jeans. Boy was I COLD.)
Sim racing WILL improve your karting - no worries. Youll learn lines (a lot more than on the track), and will improve VASTLY on your gut-feeling of the car - youll know just how fast you can do a bend after doing it 3 times, and will catch the kart attempting to slide out on you much MUCH faster.