Most people throw their rear torsion bars in the garbage because they’re rarely useful. They lock the rear down too hard in almost every occasion, binding the kart up and not letting it release off the corners properly.
Putting the bar in might have made the kart feel better because you were so bogged down it couldn’t release and it felt stable. Lots of times in lower horsepower classes the kart can feel really stable and predictable but it’s just off the pace. And that’s because it’s got too much grip in the chassis and it’s not letting the kart roll on corner exit. It won’t slide because it’s all bound up. So it feels better but it’s much slower. I know this isn’t a lower horsepower kart but it might apply here as well.
Sliding and out of control loose isn’t fast, it’s equally slow as being tight and locked down. But you need the kart to lift, rotate, and release and be on the edge a bit to be quick.
Given that you’re relatively new, it very well could just be your driving or line. How consistent are your lap times?