Mercury 4stroke 2018 80hp will not max rev, only getting 3/4 of power

[ulfie81]

Hello friends!


I have a problem. From one boat ride to another (not gradually getting worse or anything) my mercury will not operate properly. Between those boat rides was about three weeks of bad weather so the boat was laying at the dock.

So, what happened is: engine runs fine at idle, accelerates as usual but my "Full throttle” is about 3/4 of what it should be. It runs fine at that 3/4 but I am missing 10-12 knots of speed. This is not a fast boat so it is kinda annoying to lose one third. I am now at top speed around 22-24 knots, originally it should be 33-34 knots. It is not stalling or bogging or nothing butI will not get top speed. Usually if at WOT my RPM is 5500-5700 but now I am at around 4500.

I cleaned the hull from some barnacles, gained a knot or two, changed water separator, checked the in line fuel filter, looks ok, however, under the cowl it is a bit damp but I think it is from winter conservation
Prop is not tangled. Fuel consumption is the same as when I reached top speed or even maybe a little bit higher

Serviced as it should, last Service( 300h service; impeller, plugs, filter etc) after last summer so it is due in a couple of months

You guys have any thoughts? I do not want to take the boat out of the water, take it to the shop and all that f not completely neccessary


Thank you so much

Brgds U

 

[TheKarnicKid]

Is this mechanical throttle linked or 'fly by wire' please

 

[ulfie81]

looks like linkage "in engine", from throttle lever at the helm to engine i presume it is wire

 

[colhel]

When you say you cleaned some barnacles, did you jet wash/clean the whole hull?

 

[ulfie81]

When you say you cleaned some barnacles, did you jet wash/clean the whole hull?

I use a brush, whenever we beach the boat, I walk around and brush the hull, pretty agressively . Then touching the hull with my hands to feel if any left ( it is a pretty small bowrider)

 

[TheKarnicKid]

looks like linkage "in engine", from throttle lever at the helm to engine i presume it is wire

If it is wire and is fuel injected and not carburettor,most likely will have in built diagnostics,a check on fault codes would
help to rule out the motor being at fault.

 

[ulfie81]

If it is wire and is fuel injected and not carburettor,most likely will have in built diagnostics,a check on fault codes would
help to rule out the motor being at fault.

You mean I can attach like an OBD device? because I only have the Smart craft rev counter and speedometer. I got a message on this saying : stbd emergency stop, that dissappered as quickly and never been seen again. google didnt help more than maybe a lanyard-problem, flipped the lanyard a couple of times. seems to work

 

[jonbclarke]

The Stbd Emergency Stop is just telling you that the engine has been stopped someone pulling on the lanyard. It should clear but will stay saved in the memory of it.

Any dealer should be able to plug into the engine to tell you whether there's any current or non-active fault codes, it's basically the same principle as OBD but a different connector and software so you can't do it yourself. Dealers have to pay a £££ to get access to the system every year so expect to pay a little for their time and access to the kit but most won't charge more than about half hour labour for a computer plugin if you can bring the boat to them.

That said as @TheKarnicKid suggests, based on what you've said it seems quite likely to be environmental (hull, prop or fuel) so if I were you I'd just double check you've exhausted those options first.....

 

[ulfie81]

The Stbd Emergency Stop is just telling you that the engine has been stopped someone pulling on the lanyard. It should clear but will stay saved in the memory of it.

Any dealer should be able to plug into the engine to tell you whether there's any current or non-active fault codes, it's basically the same principle as OBD but a different connector and software so you can't do it yourself. Dealers have to pay a £££ to get access to the system every year so expect to pay a little for their time and access to the kit but most won't charge more than about half hour labour for a computer plugin if you can bring the boat to them.

That said as @TheKarnicKid suggests, based on what you've said it seems quite likely to be environmental (hull, prop or fuel) so if I were you I'd just double check you've exhausted those options first.....

thank you, i will take it to the dealer for sure when it is time for yearly service in the end of september
Just hoped there was some things I could try first on my own to get it running better

I changed the water separator, I have purchased a new In-line fuel filter and I will check the spark plugs but that is the end of my knowledge

 

[colhel]

Just reiterate, make sure the hull, prop and outboard leg are as clean and smooth as you can possibly get them.

 

[ulfie81]

Just reiterate, make sure the hull, prop and outboard leg are as clean and smooth as you can possibly get them.

Will do, a lot of barnacles this season, more than past seasons, we launched the boat earlier this year so that might play in. But I always brush the hull when the wife is at the beach sun bathing, first time a lot of barnacle particles whirled around but now not that much so I think the hull is pretty clean

 

[ulfie81]

got another "tip" from a youtube video from Reel Life Fisherman, see below image, the white plastic ring have something to do with the exhaust and when it gets worn out you can lose top speed/rpm. so might try changing this when replacing prop with stainless ( probably after season)