Lower Unit?

[sybaris2]

Took the boat out yesterday for the first time this season. Let her warm up then around the lake at idle for about 45 minutes. Started a full speed run, all the gauges were fine but didn't get up to more than 20mph. Took her back down to idle and went back home. Couldn't do any troubleshooting cause had some guests but plan on taking her out this evening to try to determine the issue. Any tips on things to do to narrow down the cause much appreciated.

--------------------
2005 Crownline 220EX
260HP 5.0L Merc
B3

 

[Texasmark]

First wild guess would be old gas. Has a way of really making a good engine run crummy!

 

[Scott Danforth]

I agree that it is most likely crappy fuel

 

[sybaris2]

I agree that it is most likely crappy fuel

Crappy fuel even though the RPMs were good?

 

[nola mike]

Crappy fuel even though the RPMs were good?

If the rpms are good and the speed isn't, you either have a dirty hull, or are carrying a ton of extra weight. Maybe spun prop depending on exactly what it's doing

 

[dubs283]

Crappy fuel even though the RPMs were good?

you didn't post any rpm readings

 

[sybaris2]

If the rpms are good and the speed isn't, you either have a dirty hull, or are carrying a ton of extra weight. Maybe spun prop depending on exactly what it's doing

If she's not in use then she's on a lift. Nothing on the hull except a mirror shine. Was carrying half capacity

 

[nola mike]

If she's not in use then she's on a lift. Nothing on the hull except a mirror shine. Was carrying half capacity

Waterlogged boat always a consideration, sounds unlikely in your case. Physically impossible to turn the same rpms at lower speed unless you increase slip.

 

[sybaris2]

Waterlogged boat always a consideration, sounds unlikely in your case. Physically impossible to turn the same rpms at lower speed unless you increase slip.

It's looking more like the coupler is shot as I did smell something like burnt rubber when it happened.

 

[JASinIL2006]

If you find any little black rubber bits/crumbs in the bilge, that would seal it as the coupler.

 

[nola mike]

Usually once the coupler goes you won't get back to full speed and won't be able to hold rpm without slipping. I didn't get that sense from your post, but hard to tell rereading it.