with the air temp rising , the air density drops causing a drop in performance.The first thing I would do is to add a Phenolic spacer,1 or 2 " high ,that would keep your fuel much cooler passing trough a much cooler carburator.20 -30 degrees is not a lot to effect performance. I run my boat in hotter wheather occasionally without much loss in performance.The Dodge boys introduced the phenolic bodied Thermoquad carb back in the seventies with great sucsess [my 72 Challenger had it] and my 96 Mustang GT, Corvettes,Mercedeses and other makes turned to composite intakes for smoother runners and cooler fuel delivery to gain a few horses.The ambient temp is always lower in a boat than a car anyways, providing you have good ventilation under your enginebox [if you have one].