Go kart myth. Bigger engine=faster go kart
Truth. All industrial 4 stroke engines are governed to about 3600-3800 rpm max. Rpm dictate speed, not engine size.
Predator 212 hemior non hemi, Subaru ex17, Briggs 5 hp flathead, tecumseh OH60, Honda gx200, greyhound honda gx 390, gx670, predator 420, predator 670, whatever. They all operate at governed rpm of 3600 ish.
Bigger engines can be geared differently as they won't stall as easily under load. So a predator 212cc with 30 series is great for a small or moderately sized kart up to 35ish mph.
Anything 8-18 hp can be geared on larger karts with 40 series up to 40 mph.
These are general guidelines based on my own opinion, which comes from my observations of popular karts from the 90s-2000s