My 99 25hp Merc is having a couple issues: First, intermittently after running at speed, when I come back to neutral it will idle way above normal RPM. This started several weeks ago. Now as of yesterday it will not hold at anything close to WOT. Idles good (with the above exception), comes out of the hole fine, then as I start to trim her out she will slowly lose RPM. Is a little carb work in order?