Weird - that’s exactly the scenario I was in when I jumped down the rabbit hole of trying to solve this very issue by swapping ignition coils/maps after trying most of the less drastic options. Ultimately, I ended up never being able to impact things as much as I would like because all of these kart engines are designed to do well on mid/top end tracks (aka like the majority of European tracks and the national-level tracks in the US), and with regulations being what they are there isn’t enough adjustability in the platforms to truly change the bias. (for instance, a fully adjustable ignition map could do the job)
None of that is to say that the performance can’t made a bit better than it would be otherwise on even the tightest track, just that you’re swimming upstream with something which was fundamentally built for stretching its legs. But at least you have the gearbox. I’ve kind of been lamenting my decision to not go the gearbox route the last time I choose a new engine package. 