I have a 2001 mercury 250 saltwater efi on my 25' proline walkaround. I normally run @ 5000 rpms, burn 22 gph and go around 23 knots. Lately when I first start going my wot is only around 5000 rpms and my fuel guage shows I'm burning like 28 gph. Sometimes when I drop to neutral and go again the problem disappears. Sometimes it doesn't, but after a running some more I will fill the rpms kick back up and everything will be fine again. It feels almost like it is not running on all cylinders. I changed the plugs and same thing. Any ideas??? Can it be a thermostat issue?
