tracker 40 won't throttle up under load

[kevmyers]

I bought a used Tracker 40, installed it on my 18ft. pontoon and it worked great the first year, one day without warning it would only rev to about 3000rpm at full throttle (in gear). However, when tied up and in neutral it will rev all the way up. I am not sure if it is the linkage or possible clogged carbs? I tried to remove the carbs but got stuck at the rubber gromets that are attached to carbs and go throug the backing plate. Is there a trick to removing without ruining the rubber inserts? More importantly, any ideas of what the problem is caused from?

[boats.net]

Could need carbs removed and cleaned, or loosing fire on a cylinder. Need to run a compression test.