Losing some RPM and top end

[Bdsp1234]

So.... I have a 2001 , Yamaha 200 HPDI. This motor is and has been extremely reliable however I’ve noticed a drop off in performance. I started the season with 5400 rpm and 39mph at WOT. Now top end is 5000 RPM and 34 MPH.

Boat is a 2001 226 with hardtop.

The boat has been wet slipped all summer, so I’m thinking that there may be some build up, but it seem s to be quite a drop off.

Any thought?

 

[seasick]

Does it surge or just top out at a steady rev level?It could be extra drag from growth or extra weight.
Take a look at the prop to see if it is damaged. That can be hard to do if the damage is slight like a slightly bent blade.
Check you throttle cable adjustment to make sure that the lever at the motor is pushed all the way open when the control is pushed forward
Those are the simple things.
It gets more complicated after them, like bad spark coils. Bad injector(s). etc.

 

[Doc Stressor]

I used to see a similar drop off in performance at the end of the season when I used to keep my 204c wet slipped in Connecticut. The efficacy of the bottom paint falls off over time if you are in a high growth environment. Down here in Homosassa, a lot of folks take their boats up to the springs, get in the water, use a pot scrubber to remove the slime off of the bottom every few months.

If you are seeing any hard growth at all on the bottom, performance will drop off significantly. Even slime will slow you down some.

 

[seasick]

If that is the cause it is easy to check in a way. Haul the boat and clean the bottom and see if the top end changes. While you are at it, take a picture of the hull before you scrub it. If it turns out that slime or grown is the culprit, I would like to know how bad the hull looked.

 

[Bdsp1234]

Does it surge or just top out at a steady rev level?It could be extra drag from growth or extra weight.
Take a look at the prop to see if it is damaged. That can be hard to do if the damage is slight like a slightly bent blade.
Check you throttle cable adjustment to make sure that the lever at the motor is pushed all the way open when the control is pushed forward
Those are the simple things.
It gets more complicated after them, like bad spark coils. Bad injector(s). etc.

Seasick, no surge at all. Just a steady rev

Does it surge or just top out at a steady rev level?It could be extra drag from growth or extra weight.
Take a look at the prop to see if it is damaged. That can be hard to do if the damage is slight like a slightly bent blade.
Check you throttle cable adjustment to make sure that the lever at the motor is pushed all the way open when the control is pushed forward
Those are the simple things.
It gets more complicated after them, like bad spark coils. Bad injector(s). etc.

Seasick, prop has no damage. I am going to have it redo end this winter but it’s ok. It’s a steady rev to 5000 RPM. I’ll have to pull it and clean and run again. I did run again today again with exact same numbers. Conditions were perfect.

 

[Bdsp1234]

Thanks all. I will have to pull and give the hull a good cleaning. Although the reduction in top end does concern me , I don’t understand the drop off in the rpm. I’m more concerned about the RPM loss

 

[kirk a]

More resistance, lower speed, and motor can't turn as fast as it should. A comparison is weight, max RPM will vary with a very light load, vs heavy load.

 

[seasick]

Kirk is correct but as you note, but it could be the other way around; lower thrust(horse power) reduces top revs and speed. The fact that the motor doesn't surge means that fuel pressure (VST) is probably not an issue.
Could be drag and you will know after scrubbing the bottom or it could be reduced spark, bad plug, underperforming injector, etc.
It could also be just old age, low compression and the like.
Clean the hull and go from there.

 

[kirk a]

One other thought I had - is this boat new to you? Have you had it for more than this year? Did you wet slip it in the past? I've been amazed in the past at how relatively little growth has such a large impact on performance.

 

[DennisG01]

Just another quick vote for a dirty bottom

What you're experiencing is very normal - and it doesn't take much growth, at all, to see the performance difference you are seeing (both speed and RPM drop).

 

[ocnslr]

Just another quick vote for a dirty bottom

What you're experiencing is very normal - and it doesn't take much growth, at all, to see the performance difference you are seeing (both speed and RPM drop).

^^^^ THIS ^^^^

Our boat was slipped for years in Norfolk, VA, and I could see decreases in speed and RPM, and increased fuel use, when it was no more than a couple of dozen small barnacles on the trip tabs. If you have any real growth - barnacles or grass - on your hull bottom, you will see exactly what you describe.

 

[wspitler]

Not familiar with the HPDI fuel system, but I wouldn't rule out partially clogged filters. Just had a similar problem with my starboard F250. No surging just limited RPM. Changed the F and VST filters and now it runs like new. I would have suspected surging as seasick mentioned, but it was steady, just reduced power.

 

[Bdsp1234]

One other thought I had - is this boat new to you? Have you had it for more than this year? Did you wet slip it in the past? I've been amazed in the past at how relatively little growth has such a large impact on performance.

Kirk, this is my first year with this boat, and yes this was confirmed by boat yard. It is being pulled this weekend and power washed. Boat yard said that as few as 10-12 barnacles could drop top end by 5 mph. Once scrubbed and powerwashed, mechanic said he feels strongly that I’ll be right back to normal. If not he said all filters etc will need to be replaced as is typical with HPDI’s

 

[drbatts]

Not familiar with the HPDI fuel system, but I wouldn't rule out partially clogged filters. Just had a similar problem with my starboard F250. No surging just limited RPM. Changed the F and VST filters and now it runs like new. I would have suspected surging as seasick mentioned, but it was steady, just reduced power.

Had similar experience with both one of my F225s and a friends. it was a slight drop in the top end rpms, engine ran fine otherwise. The culprit was a clogged C filter.