The greatest difficulty about 'big meetings' is that you only ever get to test in those conditions when you're at a big meeting. There is simply no other time when the track has layers of fresh rubber being laid down (and peeled up) by so many karts. Because the conditions are so different to a normal practice day, it can be very difficult to adapt. People often complain at the end of the weekend that "we tried absolutely everything, and nothing worked!"
This is especially galling after two full days of practice, and then a recognised star like James Sera or Cian Fothergill turns up and puts it on pole after nothing more than a carbie session.
Funnily enough, often the two days practice is actually part of the problem, especially at an unfamiliar track. As the driver first starts to learn the track, the kart doesn't do everything that he wants and so adjustments are made to try to rectify the problems. Track widths are altered, front end alignments adjusted, axles and hubs go in and out of the kart. By the time Thursday afternoon rolls around, the kart's setup is nothing like the one that works at home, no-one can remember what changes did what, and to top it all off, the driver has finally learned the track and would be doing better laptimes with the kart back in its standard setup (which is what you should do whenever you get lost, by the way).
The solution is a simple rule.
On Wednesday, you alter nothing but tyre pressures, basic track widths, and gearing/pipe. Nothing else. Nothing else! When you wake up Thursday, do your first session with the setup you used Wednesday afternoon. Now people will start breaking out new tyres, and now you can start to learn. Now the track starts to evolve into the track you'll actually be racing on, and now the changes you make might actually be meaningful. Gearing and pipe data translates pretty well from Wednesday to Sunday. Axle selection really, really doesn't.
So that's it. Don't confuse yourself. Do plenty of testing at home and have confidence in your basic setup. Make minor alterations from Thursday afternoon through to Sunday morning, but nothing more than one or two (at most) adjustments per session.
Yeah, you won't be able to try as many things... but I bet you learn more!