These are the list of heavy weight karts and how to get them.
1Standard Kart L Unlocked
2Offroader Unlocked
3 Flame Flyer Unlocked
4 Piranha Prrowler Locked-Beat Special cup 50cc Grand Prix finish first. OR play 600 games.
5 Jetsetter Locked-150cc Grand Prix Score one star or higher. Or play 4500 games.
6 Honeycoupe Locked-150cc Grand Prix finish Lightning Cup in first or play 3000 games.