The fuel filter probably needs to be replaced. It could be stalling because of a major vacuum leak. Check the PCV valve and all the hoses.
Sounds like the throttle cable is broken.
Could be a weak fuel pump or plugged fuel filter.
If the boat idles fine and revs fine in neutral in the water and idles fine on the trailer, however has no power when you stick it into drive and give it some throttle a common problem with some of these early Mercury V6's is in the stator. The only way to fix this is to replace the stator.
Probably a bad idle air control valve.
id change the coolant temp sensor
Mine did this and I found out it was the timing belt that needed to be changed.
Check the air filter, it's probably clogged.
Could be clogged converter in the exhaust system..
Sounds like a motor mount or a transmission problem.......
it is the carb. my uncles did the same thing. you need to have them cleaned and have them put in sync
Assuming you replaced the fuel filter, here are a few things to check, Spark plugs, Spark plug wires, Distributor cap and rotor,
Replace the plug wires