Well, go ahead and seal the engine any ways. (it can't hurt) I have an engine that likes to run around 240 and its not sealed, then one that likes to run at 260 - 270 and the back plate and where the carb meets the case is sealed (then I sealed the carb it self, the needles with RTV and green slime) then I have a engine that likes to run at 280 - 310 and it has the back plate and where the carb goes in to the case sealed.

I'm running 30% but about to drop to 20% or 15%