Losing some top End

2018 Merc 115 pro XS
I’ve been running as follows:
2-3 adults/ 42-44 mph, conditions pending/ 6100 rpm.
1 adult/ 45-46 mph, conditions pending/ 6100 rpm

until earlier this year. Now, I’m seeing 5900 RPM, 3 adults and couldn’t get past 38.5 mph all weekend. This year I’ve done new plugs, new fuel filter, oil change, etc etc.

Prop was modified slightly, but this issue has surfaced well after that (ie it ran fine after the shop adding some cup to the prop).

Any thoughts? I’m going to tear down the prop and hub and look to see if there’s any line wrapped up in it. Motor feels/ sounds great as usual.

I have the same motor but interested in the cupping you did. Please tell more…

Couple of quick thoughts, make sure the throttle is opening all of the way, cables can stretch a tiny bit over time.
We are seeing some of the same complaints here and believe it or not even a slightly dirty hull can cause enough parasitic drag to slow the vessel down and you will lose some revs also as the motor is struggling to push a dirty hull through the water.

Has your hull had any significant water in it recently? The foam can absorb water and add a significant amount of weight in a hurry.

If you have a spare prop I’d try that out too just to make sure it isn’t a prop issue.

Is the motor trimming up like it always has but just not revving out?

Iowaboy1 wrote:

Couple of quick thoughts, make sure the throttle is opening all of the way, cables can stretch a tiny bit over time.
We are seeing some of the same complaints here and believe it or not even a slightly dirty hull can cause enough parasitic drag to slow the vessel down and you will lose some revs also as the motor is struggling to push a dirty hull through the water.

Hot weather and old or bad fuel can impact as well.

My Yamaha 150 did this . Was dirty injectors and clogged Vapor seperator tank screen .

isu22andy wrote:

My Yamaha 150 did this . Was dirty injectors and clogged Vapor seperator tank screen .

Did you send your injectors out to be cleaned or DIY clean them?

I need to do this to my 115 Yamaha. Planning on cleaning the VST up and then running it prior to cleaning the injectors.

I just went out and checked out the prop, it’s still in good shape. Lower unit/ Skeg was a little chewed up on the back side. I just cleaned it up and re-shaped with a flap wheel. Changed the LU oil while I was there, looked great still blue as it should be with no water in it.

Crank case looks great, no water in there either thankfully (see some of my previous posts about the warranty work Merc did for me last year).

As far as I’m aware, the 115 ProXS does not have a water separating filter like the yamaha’s do. I’ve looked all around my boat (bought new in 2018) and have yet to see one anywhere. The good news is it has never been gassed up with anything but non-oxy its whole life. It has around 175 hrs on it at the moment.

I will check out the injectors, any tips for this? Heading to youtube now to see what they say

Did you get the 5 year warranty when you bought it?

In addition to suggestions above…

Put witness marks on the prop and hub And then check them after use to determine if the hub is slipping.

Personally, my first suspect would be dirty injectors.

Grouse

bigcrappie wrote:

Did you get the 5 year warranty when you bought it?

Factory 3 year.

B-man, I have been looking a lot into the foam thing lately and I know all about it. I’m planning to take up the center floorboard soon and check out the tank and hopefully get eyes on some of the foam. I had a significant amount of water in it once, 2 years ago. It has run fine since that time. What happened was I ran about 15 miles down the river through a torrential downpour.

Crappie- I had mark’s prop shop add a small amount of cup when I had him fix my prop last season. This gives me really great stern lift with the 4 blade swept cleaver I’m using from Turning Point. My ass end jumps right up onto plane even with 3 guys in the boat. I lost 1 mph when we did this, so I was down to 44-45 at warp speed at that time, however this past weekend I could only achieve 38 and I wasn’t quite able to reach 6100 rpm as I typically can at max trim.

Sheldon, Do you have literature on adjusting the throttle cable on this rig? I think perhaps I’ve got a small amount of stretch. When I placed the throttle handle in WOT position I can still move the arm in the powerhead just a little bit, maybe 1/8″ or less. But it’s not fully topped out

Sent ya a pm with my phone number, call me and I will walk you through it but you have to pay attention to what I tell ya !!

dhpricco wrote:

<div class=”d4p-bbt-quote-title”>isu22andy wrote:</div>
My Yamaha 150 did this . Was dirty injectors and clogged Vapor seperator tank screen .

Did you send your injectors out to be cleaned or DIY clean them?

I need to do this to my 115 Yamaha. Planning on cleaning the VST up and then running it prior to cleaning the injectors.

I had the dealership doing it . Im a DIY guy at heart , but I had them fix the harmonic balancer the F150s have troubles with too .

Made a minor adjustment to the throttle linkage, and cleaned up all the dings and chips on the leading edge of the lower unit/ skeg. Also cleaned up some dings on the prop that I hadn’t noticed with a file (really minor, hardly had to file anything). Hoping these changes solve the issue. Also based on feedback from a well-renowned mechanic here on IDO, going to wash and wax the bottom of the hull since it hasn’t been done in probably 2 years. Will report results when I’m done

Got out finally, re-gained about 2 mph.

Swapped to a brand new aluminum nemesis/ spitfire that I had as a spare. Got back up to 42 mph, and importantly I could top out my rpm’s at 6300 as specified by Mercury, so this tells me I’m not actually missing anything.

Thinking this may be somewhat of a prop issue, one of my blades on the stainless looks visibly a little different at the tip relative to the other 3.

Next up going to give the hull a cleaning

It’s amazing how little it takes to affect the performance of a boat. At one point this weekend I had forgot the ladder down when I headed out fishing in the morning. Topped out at 42mph with the ladder dragging. Normal top speed is 47.

I gained 5 mph once by lifting up the kicker motor .

isu22andy wrote:

I gained 5 mph once by lifting up the kicker motor .

I gained about 6mph by ditching my Ex-GF and switching to my current wife as a copilot

KPE wrote:

Got out finally, re-gained about 2 mph.

Swapped to a brand new aluminum nemesis/ spitfire that I had as a spare. Got back up to 42 mph, and importantly I could top out my rpm’s at 6300 as specified by Mercury, so this tells me I’m not actually missing anything.

Thinking this may be somewhat of a prop issue, one of my blades on the stainless looks visibly a little different at the tip relative to the other 3.

Next up going to give the hull a cleaning

Don’t forget the hull wax!

Don’t forget the hull wax!
[/quote]

Is that a thing?
I’m getting a new rig and it will sit in the water at the dock for the entire summer and I was wondering if there is something I can treat the hull with.

Eelpoutguy wrote:

Don’t forget the hull wax!

Is that a thing?
I’m getting a new rig and it will sit in the water at the dock for the entire summer and I was wondering if there is something I can treat the hull with.
[/quote]

I have always used Race Glaze or something similar and yes it helps keep the yuck off the hull. Then clean it with Muratic Acid if needed in the fall and add another coat of glaze.

Thanks John,
I’ll give that a try.

New rig to tell?

Eelpoutguy wrote:

Don’t forget the hull wax!

Is that a thing?
I’m getting a new rig and it will sit in the water at the dock for the entire summer and I was wondering if there is something I can treat the hull with.
[/quote]

I would stay clear of the pure muratic acid!! That stuff is supper mean! They have some other stuff that’s safer for aluminum hulls. Zing is what I use on pontoon toons and lower unit it melts the Mississippi slime off it!! There’s two different versions one for motor and one for aluminum.

My tritoon sits in a marina all summer. The zebra mussels build up under the toons pretty thick. I must lose at least 10 mph by the end of the summer. Yes I should take it out once a month to power wash them off, but no, I don’t have time.

gregory wrote:

I would stay clear of the pure muratic acid!! That stuff is supper mean! They have some other stuff that’s safer for aluminum hulls. Zing is what I use on pontoon toons and lower unit it melts the Mississippi slime off it!! There’s two different versions one for motor and one for aluminum.

We have always used diluted muratic acid as per the directions on the bottle and yeah it is nasty stuff, never had an issue though. Have not tried Zing I will check it out. My boat does not sit in the water much so I have not had to do this for a while. Growing up we had a camper on a lake so we did have to clean that boat well every fall and the acid did the trick real nice.

Put it on a lift. Its pretty easy to tell which boats sit in the water for extended periods of time. They all develop this obvious skum line on the hull. If the skum line gets really bad, acid will be the only solution. Make sure you wear gloves, a mask, and have a method of catching that nasty stuff while washing. Allowing it to just “go down the drain” is extremely unsafe.

A pontoon is a completely different story. They’re not really designed to be trailered all over. They do better just sitting at the dock all season lol

John Rasmussen wrote:

<div class=”d4p-bbt-quote-title”>gregory wrote:</div>
I would stay clear of the pure muratic acid!! That stuff is supper mean!

We have always used diluted muratic acid as per the directions on the bottle and yeah it is nasty stuff, never had an issue though.

FYI – muratic acid will make both 304 and 316 s/st corrode in a matter of hrs. It removes the passive layer and will cause rusting, pitting, and discoloration. Don’t mix the two…