I work in an indoor kart track where our `best` karts are 270cc sodi karts. In any of our karts (few different chassis etc) the quickest laps are always done by being smooth and keeping the engine revs up. At the moment after only 30laps on our current track I'm a tenth off the lap record, set by someone who has done 100s of laps. He is a regular and noticed how I setup the kart into the corners, asked me some Qs and now after a few visits is used to the way I drive our circuit and on my pace.
My advice to any drivers looking for a quick time is to keep braking to a minimum as the karts aren't going that fast so the front tyres usually scrub off enough speed to make the apex. Keep the kart controlled, no point sliding a puny little 4 stroke that weighs the best part of 200+kgs as it will not accelerate quick enough. Keep your steering to minimum, the straighter the kart the less work the engine has to do.
From my experience of marshaling the biggest time killer is people stomping the brakes. They may gain a very small margin in hairpins by going in quicker and still hitting the apex, but by the time the engine winds up again they've lost so much time.