[J Persons]

It's probably heat soak into the carb. My car does the same thing in the summer when the air temp is over 100. About the only cure is to isolate the carb from the engine using an insulated spacer, or a turkey pan that seals against the bottom of the hood. Holley sells an aluminum plate and spacer that is probably better than thean insulated spacer by itself, but still probably not as good as a turkey pan.