I found RT carbs do not like high heat/humidity, with a lack of adjustability, and will cause motor to 4 stroke.
Drag racers get better times as the night cools the atmosphere,
Cooler air is more dense, as hotter air is thinner leading to over rich.
I do wonder if high humidity helps to act a little like water injection, which has been used to help pinging?
But I agree 4 stroking is unlikely an ignition problem,