1,000 more rpm's why?

[lakegeorge]

we bought a 2006 sweetwater 21' with a 60hp Yamaha 4 stroke, it has a 14x11 alum prop that turns at 5600 wot and 21 mph on my gps. The boat runs & handles great. We bought it 7 weeks ago and it had 1/2 tank of gas in it and I don't know how long it sat before we bought it.
We have just put our 2nd tank of gas in it this week and we went out today for an hour or so and coming in the tach is now hitting 6600 rpm's and it is running faster. I didn't bring the gps but its obvious it's running faster.
Now i'm wondering what caused this and should i get another prop to cut the rpm's down and hopefully keep the increased speed?
Any ideas are welcomed.

 

[robert graham]

Re: 1,000 more rpm's why?

maybe check speed with GPS at 6600RPM....maybe an issue with the tach, they're very sensitive to loose wires/connections. if not the tach then maybe re-prop for 5500, because 6600 not real good for motor...my opinion

 

[99yam40]

Re: 1,000 more rpm's why?

have you hit or damaged the prop in any way? If not I would think the tach may have a problem, but you need to have it checked out with a shop Tach or a different TACH of some type to see if it is accurate. the motors have RPM limiters on them and I do not think it would get that high

 

[lakegeorge]

Re: 1,000 more rpm's why?

you are correct, 5600/5800 is what manual calls for that's why I'm concerned as to what is causing this. I will call the shop that I deal with tomorrow and talk to them.
I haven't hit anything with prop theres not even a ding in it.