I have a low hour 2002 mercury bigfoot 25 HP 4 stroke. The last couple of times I have taken it out I have to really move the throttle forward to get it to start. When it does start it idles really slow. I can only get about 5 miles an hour out of it at full throttle when I could get 15 before. When I am about 3/4 through the throttle I don't get any more power going to full throtle. When I put it into neutral it seems to sound fine. Any ideas where I should start? Thanks