"I have a 2005 Mercury Saltwat
"I have a 2005 Mercury Saltwater 150 HP on a 21 foot offshore boat. The previous owner only put the boat in the water a couple of times and the boat and motor look as if they were never used. Here is my problem: When I slowly go from idle speed to about 1/2 throttle, or 2500 rpm, the boat is slow to get on a plane, and the rpm's spin up to about 4000 with little or no acceleration. The engine makes a bit of noise and the rpm's fluctuate until the boat gets onto a plane. Once it does, the rpm's stabilize and the rpm's come down, despite the boat speeding up. It sounds like the motor is laboring excessively to accelerate and it exhibits some vibration, even at slow speed. The lower unit and prop do not appear to have EVER hit anything but could the hub be defective? If I hammer the throttle from idle to pull a skier, the boat seems to accelerate better, but when I leave a no wake zone to a 25 MPH zone, the motor makes this noise and doesn't behave. When I get home and flush the motor, the motor runs perfect, accelerates perfect, and maitains rpm. It only performs poorly under load. Any ideas?"