Hi, I have a 2004 Key West 223 CC with a Yamaha 250, that has run to 57 MPH as measured by my GPS. Recently the motor runs fine, WOT is normal at 6100, but my top speed measured by the same GPS, has slowed to about 42. I have changed the plugs, the bottom is clean, the prop is clean, and I am carrying the same wieght as always. Ideas?

Thanks

Thanks for your reply. I would understand if I couldn't get from 53 to 57, I would agree with the impact of heat and humidity, but I am running 13 MPH slow. It would seem like there is more different than my trimimg, would you agree? I will check for trim this weekend when I boat again. Thanks again.

Fluke reading on GPS before?

Prop hub slipping??


Different load in boat??

have you lost compression?

How many hours on motor? Have you ever had a yamaha before? If not you need to run some "ring free" through it every season or about 100 hrs. Ask your yamaha dealer about it.