You’re already below 1/2 gph why should you be concerned about fuel burn?
I had an A25 with 34hp but don’t remember the prop size. Very similar to yours tho.
First thing to do is get familiar w the boat/engine and when you determine all’s well re propulsion take out the boat and advance the throttle to WOT .. wide open throttle. Make sure your control linkage permits and achieves WOT. Run for 30 seconds to one minute.
Look up your rated power output and observe what rpm it is achieved. If your rated power rpm is what it says it should be (or a hundred rpm over) you’re good to go. If you’re 100 rpm too low (under the rated rpm) you’ll probably want to take an inch of pitch out of your prop. Show the prop to a good (check around) prop man and determine if the prop is suffering pinkness (ask him) or is too thin or if it is “worn out” for whatever reason like too many pitch changes in the past you should consider a new prop.
North Western Washington State USA