RMP questions 115 Mariner

[davidf5252]

Hello all,

I just bought a new (used) boat 16'6 fiberglass bass boat and it has a Mariner 115hp on it...runs good...but some times there is a slight hesitation from a dig or from half throttle to full throttle...Should I run some seafoam through it???

Also...the tach works and on smooth water and trimmed up she turns 5000-5200 BUT a few times she would all of the sudden get to 5800-5900 and she WAS MOVING!!!

Why would it not go 5900 all the time at WOT?

We guess the boat was running 55 mph???? no GPS and speedo doesn't work but my dad and i have owned boats and it is just a guess....

Oh and one more thing...I pt 10 gallons in her yesterday and ran half throttle to wide open for about 1.2-2 hours and she EMPTY when i put her on the trailer..I mean BONE dry!!! is that normal???


Thanks for your input!!!

 

[davidf5252]

Re: RMP questions 115 Mariner

Ttt :d

 

[j_martin]

Re: RMP questions 115 Mariner

Running right, she'll burn 11 gallons per hour at WOT.

It should run up to top speed all the time. If it doesn't something is wrong. If it's fuel delivery, you can very easily burn down the powerhead running it like that.

There's many threads on the subject, both here and on other boards. Long story short, the bigger mercs need quality gas, a free flowing, pinhole free fuel hose and primer bulb, (Aftermarket stuff usually doesn't cut it) , clean tight fuel pickup tube, proper tank venting, Clean fuel filter, and fuel pump maintenance kept up.

hope it helps
John

 

[davidf5252]

Re: RMP questions 115 Mariner

yes all of that helps.

I run 93 octane in her.
The fuel has has a primer bulb with no leaks
The tank does not leak

I assume the pickup works....i will have to get a manual to figure out where the fuel filter is so i can change it....

any other advise guys?

 

[davidf5252]

Re: RMP questions 115 Mariner

I took her out again yesterday and the same thing...bogs down from a dig and then only reaches 5200 RPM....

I guess i can try and put a new fuel hose on and run some seafoam through it...maybe change the plugs....

the boat sat for a year before i got it...

help....

 

[j_martin]

Re: RMP questions 115 Mariner

The same symptoms will present if you have the wrong prop on it. Too high a pitch.

Check the numbers on the prop, tell us about your boat, and we can figure out if it's reasonable.

hope it helps
John

EDIT. didn't notice it ran right sometimes, prop should be OK.
That said, a bilge full of water would do it also.

John

 

[davidf5252]

Re: RMP questions 115 Mariner

The same symptoms will present if you have the wrong prop on it. Too high a pitch.

Check the numbers on the prop, tell us about your boat, and we can figure out if it's reasonable.

hope it helps
John

EDIT. didn't notice it ran right sometimes, prop should be OK.
That said, a bilge full of water would do it also.

John

I cant recall the name of the prop but my dad said it was a very high end brand.... i can look when i get home...

It only hit 5900 RMS twice in the 3 outings the boat has been on and that was only for a minute or two and then back to 5200.....

Bilge full of water??? what does that mean???

Also, the boat is 16'6 fiberglass bass boat with a full deck, console, trolling motor and a Mariner 115hp i think the boat and motor are both 1988-89 models...Where can i check to see what year the motor is.

Could this be caused by carb issues, plugs??? Also is is slow out of the hole as in the rpms when floored are at like 2500-3k and then it finally picks up..

and yes before any on ask i know how to trim the motor up when trying to reach top speed...trim down for hole shot trim up as accelerating...

Thanks for the help thus far!!

 

[j_martin]

Re: RMP questions 115 Mariner

Bilge full of water??? what does that mean???

Bilge is the bottom of the boat, and water is water. Sometimes when a boat is doggy, it turns out to be wet core, or foam, or floor, or transom, or all of the above.

With the boat dead level on the trailer, and the motor trimmed level, what is the height of the propshaft centerline compared to the bottom of the pad.

If you hit the 5900 when there was a decent ripple on the water, your motor could be set up a little too deep.

You could have performance issues because of tired plugs, or dirty carbs. If it's the carbs, you could permanently hurt the powerhead by running lean.

John

 

[davidf5252]

Re: RMP questions 115 Mariner

OK the PROP is a Quicksliver laser II 20P

Could this cause it to not spin at 5800-6000 RPMS? How much is it worth and what prop do I need to get the most speed? Should I raise my motor up? Could this be causing it not to get out of the hole good?

This is my bass boat but i will be pulling tubes, wake board....and as it stands right now she wouldnt pull a ski'er or wake border out on the hole shot i dont think...

 

[j_martin]

Re: RMP questions 115 Mariner

I run an XR4 on an 18' Fish N Ski boat. I run a 24 pitch high five most of the time, and it can pull up a skiier. However, when I plan to haul a load like that I go to a 22 pitch high five. It just gives me better control of things. I have enough power to make a teenager scream "slow down", and I change props to meet conditions. You are certainly not overpowered, so consider that you won't get the best of all worlds with only one prop, and no effort.

The Laser II is designed as a top speed surface piercing prop. If you run it deep, It'll suck on the top end. If you run it where it wants to be, it'll have a mediocre hole shot. It is not a ski boat prop by any means, it's a flat water top speed speed prop.

I don't know your setup, so I can't tell, or even guess how it's affecting how your boat is running. I asked some pointed questions to get the information that might solve the puzzle.

1. Were you in choppy surface, fast running conditions when you noticed it get up and go, or was it smooth water? It's possible if your setup is marginal that it just got "loose" and flew for a change, like it's supposed to. On the other hand, if the conditions at the time would deem that unlikely, no amount of setup is going to remedy your engine mechanical problem.

2. What is your present engine height, and is it bolted to the transom or set back. That'll tell me if it is at least reasonable.

I suggest you read up on prop selection and boat setup. If you're going to push the limits of performance, it might help to have a manual jack plate so you have very fine adjustment of engine height. At the least, you'll need 2 props to cover all you want to do with it.

It's all money. I chose to put on a high five, and I shopped around till I found a good used one at the right pitch. I had another damaged one that I had repaired and put into service. I could get more speed out of the boat, but I chose to compromise on the side of service and handling. I still get within a few MPH of the top speed capable with this hull, load, and engine by proper setup.

hope it helps
John

 

[davidf5252]

Re: RMP questions 115 Mariner

I run an XR4 on an 18' Fish N Ski boat. I run a 24 pitch high five most of the time, and it can pull up a skiier. However, when I plan to haul a load like that I go to a 22 pitch high five. It just gives me better control of things. I have enough power to make a teenager scream "slow down", and I change props to meet conditions. You are certainly not overpowered, so consider that you won't get the best of all worlds with only one prop, and no effort. that is pretty cool

The Laser II is designed as a top speed surface piercing prop. If you run it deep, It'll suck on the top end. If you run it where it wants to be, it'll have a mediocre hole shot. It is not a ski boat prop by any means, it's a flat water top speed speed prop. So this prop when the motor is trimmed all the way down could make it bogg coming out of the hole? should i trim it up like im running down the lake at WOT for the hole shot? I was always told trim down, hit gas then trim up as it is moving for best performance with any boat??

I don't know your setup, so I can't tell, or even guess how it's affecting how your boat is running. I asked some pointed questions to get the information that might solve the puzzle.

1. Were you in choppy surface, fast running conditions when you noticed it get up and go, or was it smooth water? It's possible if your setup is marginal that it just got "loose" and flew for a change, like it's supposed to. On the other hand, if the conditions at the time would deem that unlikely, no amount of setup is going to remedy your engine mechanical problem.

when it 5900-6k it was in smooth water trimmed all the way up

2. What is your present engine height, and is it bolted to the transom or set back. That'll tell me if it is at least reasonable. I dont know the height...it is mounted to something and it has 5 holes on each side i think it is mounted in the middle hold and could be moved up 1/4 - 3/4 of an inch

I suggest you read up on prop selection and boat setup. If you're going to push the limits of performance, it might help to have a manual jack plate so you have very fine adjustment of engine height. At the least, you'll need 2 props to cover all you want to do with it. I just want it to not bog down out of the hole and spin 5900 RPM so i can haul butt at 55+ mph

It's all money. I chose to put on a high five, and I shopped around till I found a good used one at the right pitch. I had another damaged one that I had repaired and put into service. I could get more speed out of the boat, but I chose to compromise on the side of service and handling. I still get within a few MPH of the top speed capable with this hull, load, and engine by proper setup.

hope it helps
John

my answers in red....

 

[j_martin]

Re: RMP questions 115 Mariner

So this prop when the motor is trimmed all the way down could make it bogg coming out of the hole? should i trim it up like im running down the lake at WOT for the hole shot? I was always told trim down, hit gas then trim up as it is moving for best performance with any boat??

The prop is designed to pierce the surface when it's running. That means running level with the boat, and part way out of the water. It is a top speed racing type prop. To get any hole shot at all, you have to trim it in, but you will never get an optimum hole shot out of this prop. Your engine probably can't properly surface this prop without low water pickup modifications to the LU, either a transom mounted water pickup, or a LW pickup nosecone.



when it 5900-6k it was in smooth water trimmed all the way up

That's normal running. You have a mechanical problem with your motor. You could fix it now, or wait till a piston melts and know which carb it was. If it's electrical, it probably won't eat a piston.



I dont know the height...it is mounted to something and it has 5 holes on each side i think it is mounted in the middle hold and could be moved up 1/4 - 3/4 of an inch

It all depends on where the rigger drilled the holes in the transom. That's why you have to measure it.



I just want it to not bog down out of the hole and spin 5900 RPM so i can haul butt at 55+ mph

Once the motor is running right, and mounted right. Put on a high five, (20 inch probably) and settle for 53, or else put up with the poor hole shot.

hope it helps
John

 

[davidf5252]

Re: RMP questions 115 Mariner

"when it 5900-6k it was in smooth water trimmed all the way up

That's normal running. You have a mechanical problem with your motor. You could fix it now, or wait till a piston melts and know which carb it was. If it's electrical, it probably won't eat a piston."

So I know that 6k is normal...but it only did it twice in smooth water... it turns 5-5200 all the time in choppy/rouch water and some times on smooth...

So you think i have a carb(s) issue? as the boat sat for a year...

This is only my second boat...and the first was a 1956 johnson javelin 30hp and i could work on it... i dont want to attempt to try and work on this one...

So do you think seafoam stuff will clear up the carb issue if that is what it is?? or do I need to rebuild the carbs? it idles perfect and only bogs down some times but other than that im just looking for those RPM's i DO NOT want any major damage to occur and if you think something is wrong i wont run the boat again until i get it sorted out...

Also should i keep it trimmed down for the hole shot or based off the designe of the prop raise it up a good bit?

 

[davidf5252]

Re: RMP questions 115 Mariner

"Your engine probably can't properly surface this prop without low water pickup modifications to the LU, either a transom mounted water pickup, or a LW pickup nosecone."

HUH? Well trimmed up it still pees perfect so I know water is getting in there... but could post a link to what ever you're talking about? I dont know anything about boats

Oh and THANK YOU SO MUCH FOR ALL THE HELP... I can also take measurements if you tell me what to measure when i get home..

 

[j_martin]

Re: RMP questions 115 Mariner

So I know that 6k is normal...but it only did it twice in smooth water... it turns 5-5200 all the time in choppy/rouch water and some times on smooth...

So you think i have a carb(s) issue? as the boat sat for a year...

This is only my second boat...and the first was a 1956 johnson javelin 30hp and i could work on it... i dont want to attempt to try and work on this one...

So do you think seafoam stuff will clear up the carb issue if that is what it is?? or do I need to rebuild the carbs? it idles perfect and only bogs down some times but other than that im just looking for those RPM's i DO NOT want any major damage to occur and if you think something is wrong i wont run the boat again until i get it sorted out...

All I know is that is when it ran like it should. Something is wrong. You could try the sea-foam. Nothing lost but a 6 dollar can of additive. I might clean out a mildly dirty passage in a carb, but it won't fix anything mechanically wrong, or even get real dirt out.

If the problem is that a cylinder or 2 is leaning out, it could indeed cause major damage. That's why the major priority should be to find out what is wrong.

At this point, a litany of what you have tried on the engine, and the results might be helpful.


Also should i keep it trimmed down for the hole shot or based off the designe of the prop raise it up a good bit?

You need to bury it to get the stern out of the water on the hole shot. It's just that that prop will probably load up at hole shot time, because it's optimized for top end.



HUH? Well trimmed up it still pees perfect so I know water is getting in there... but could post a link to what ever you're talking about? I dont know anything about boats.

You're running that prop fully submerged just below the surface, and angled upward significantly. It is designed to run level, and piercing the surface, or running about 2 inches out of the water. Your engine is probably mounted 2 inches or more too low for that prop. If it were mounted right, you wouldn't have any water pressure and would probably burn up the motor without a low water pickup of some kind. That's why I think you might get nearly the same top end performance, and much better hole shot out of a prop designed to pull a relatively heavy load efficiently. A vented 4 or 5 blade prop.



I can also take measurements if you tell me what to measure when i get home..

Propeller shaft height to pad relationship, detailed in an earlier post.


Oh and THANK YOU SO MUCH FOR ALL THE HELP...

You're welcome.

 

[davidf5252]

Re: RMP questions 115 Mariner

"
If the problem is that a cylinder or 2 is leaning out, it could indeed cause major damage. That's why the major priority should be to find out what is wrong."

what could it be? how do i diagnose? Do i have to take it to a shop?? Id rather try and do the work myself with a manual if it is not to advanced...

and you answered my other questions...I was just trying to avoid buying another prop...skiing is not my priority, bass fishing is

either way i can still pull a tube as i dont need a good hole shot for that

 

[j_martin]

Re: RMP questions 115 Mariner

what could it be? how do i diagnose? Do i have to take it to a shop?? Id rather try and do the work myself with a manual if it is not to advanced...


2 cycle is easy. It goes squish-bang. If you have compression, fuel-air at the right mix, and spark at the right time, it goes. Reeds only affect low speed. They stand wide open all the time at half speed or more.

Here's where I need the litany of what you have done so far.

Compression test
Spark test on all cylinders
DVA tests on stator, trigger, and switchbox
On the fly spark testing
Looking for leakage in the kill circuit.
(that about covers electrical)

Fuel pressure monitoring
As needed, fuel system parts.

It's really a pretty easy motor to work on. Carbs are simple. DVA is a special meter or adapter for a standard meter. What it is --- a peak reading voltmeter.


As you figured out, prop and setup are always a compromise.

hope it helps.
John

 

[davidf5252]

Re: RMP questions 115 Mariner

what could it be? how do i diagnose? Do i have to take it to a shop?? Id rather try and do the work myself with a manual if it is not to advanced...


2 cycle is easy. It goes squish-bang. If you have compression, fuel-air at the right mix, and spark at the right time, it goes. Reeds only affect low speed. They stand wide open all the time at half speed or more.

Here's where I need the litany of what you have done so far.

Compression test
Spark test on all cylinders
DVA tests on stator, trigger, and switchbox
On the fly spark testing
Looking for leakage in the kill circuit.
(that about covers electrical)

Fuel pressure monitoring
As needed, fuel system parts.

It's really a pretty easy motor to work on. Carbs are simple. DVA is a special meter or adapter for a standard meter. What it is --- a peak reading voltmeter.


As you figured out, prop and setup are always a compromise.

hope it helps.
John

I have done any of that... i guess i need to get busy... how do you check the spark on those kinds of plugs? thanks

 

[eullnj]

Re: RMP questions 115 Mariner

What's the max RPMs for this motor? I didn't see the year or any mention of 2-stroke or 4-stroke (maybe I missed it). If this is the older, late 90's/early 2000's 2-stroke (non-optimax), aren't the RPMs supposed to max out around 5,250? I think there's a sticker on the motor that says what max RPM should be. Might want to check that to see if 5,900 is too high.

I've had my RPM gauge go goofy from time to time and say RPMs are higher than they actually are. Knocking my knuckle on the gauge usually fixes that problem.

Just an idea...

 

[eullnj]

Re: RMP questions 115 Mariner

Also, the bog-down problem out of the hole sounds consistent with this motor being the 2+2 115, where only the top two cylinders fire until the motor gets to somewhere around 2,000RPM, and then she takes off. Again, if that's the case, there isn't much to be done about that, I don't believe.

Look up 2+2, and you'll find a plethora of information.

In other words, it sounds like your engine might be running normally, save the RPM gauge giving you a potential false reading at 5,900.