Ask the mechanic if he will provide full warranty if any damage occurs running on that lean a mix! 🙂
Not all mechanics actually know what the heck they are talking about.
Little side story. Last week I had trouble with my Tower of Power, 115hp Merc. It would not run above a fast idle.
A Mercury Master Tech told me that it was because I had 87 octane in my tank!? Huh.
It ended up being the stator was shorted, but you get my point.