A Saito 91 is on the thirsty side as 4 strokes go. Not as thirsty as maybe an 82A (that thing drank fuel like beer! )

I would say you're pretty much ran in so I suggest you get tuning that engine for power and economy.

Put a tach on it, hit max RPM's and dial it down around 3-400 rpm and if (as it sounds) you're on the rich side now, you should notice an improvement where flight time is concerned.