RMP questions 115 Mariner

[j_martin]

Re: RMP questions 115 Mariner

Thanks!!!

I am on hold with a marina and described what was going on what RPMs it is turning and i toldhim what prop i had...

he said that 20P prop will make it bogg out of the hole and lose RPMs on the top end he said i should drop down to an 18P is he yanking my chain to make a sale?

Don't get educated by sales. It's way too expensive. Like I said before, part of the problem is that the prop is not a hole shot prop. Let's figure out just what's happening, or are you made out of money?

John

 

[davidf5252]

Re: RMP questions 115 Mariner

no money...

So what course of action do i need to take?

check compression, fuel hoses, change plugs, check spark? (does auto parts store carry these for boat, how do they work?)

 

[davidf5252]

Re: RMP questions 115 Mariner

oh and they guy got mad at me bc i was asking questions and said "bring it in and we will look it at...my advice isnt free and hung up"

 

[davidf5252]

Re: RMP questions 115 Mariner

That's right. Do you have a GPS reading for how fast you go at 5200 rpm?

Concensus is that it would rather spin too fast than too slow.

John

no but if we had to guess id say 45-52???

 

[j_martin]

Re: RMP questions 115 Mariner

A 20 pitch prop, at 10% slip, 2:1 geerz, should run at 44 MPH at 5200 rpm.

5900 takes it to 50.

18 P at 5900 is 45 mph.

I suspect the prop you have is the best pitch in that style. It is, however, a prop designed for different work, that being light and fast.

Your boat is relatively heavy for that engine, and expected to perform in a fairly large range of functions. The prop should match the task.

You don't put coveralls on a preacher, or a 3 piece suit on a farmer.

hope it helps
John

 

[j_martin]

Re: RMP questions 115 Mariner

no money...

So what course of action do i need to take?

check compression, fuel hoses, change plugs, check spark? (does auto parts store carry these for boat, how do they work?)

Sure, auto parts stores carry the plugs.

If it's new to you, do the preventative maintenance stuff.

Check the lower lube, replace if at all dirty. use good stuff.
Throw in a set of plugs
replace the water pump impeller, and more if needed.

Visually check hoses and such. The little bleed hoses are critical on that engine, as they are the primary lubrication for the mains. Be sure they are in good shape.

hope it helps
John

 

[davidf5252]

Re: RMP questions 115 Mariner

A 20 pitch prop, at 10% slip, 2:1 geerz, should run at 44 MPH at 5200 rpm.

ok so will it hurt to run that prop at 5200 rpm?

5900 takes it to 50. the only way to do that would be raise the motor and instal a water cone?

18 P at 5900 is 45 mph. but this would give me the hole shot and not bog?? but i wont increase my top end?

I suspect the prop you have is the best pitch in that style. It is, however, a prop designed for different work, that being light and fast.

Your boat is relatively heavy for that engine, and expected to perform in a fairly large range of functions. The prop should match the task.i dont know how heavy the boat is...????

You don't put coveralls on a preacher, or a 3 piece suit on a farmer.

hope it helps
John

answers in red

 

[davidf5252]

Re: RMP questions 115 Mariner

so the 18p would give me a better hole shot and not bog down? but id only be able to run 45ish....

so i guess i may need to trade this prop to someone else that has a 18p???? i cant afford to buy one... right now...

 

[davidf5252]

Re: RMP questions 115 Mariner

also where can i look up this info as far as prop v boat size/weight to see theoretical speeds?

 

[davidf5252]

Re: RMP questions 115 Mariner

Sure, auto parts stores carry the plugs.

If it's new to you, do the preventative maintenance stuff.

Check the lower lube, replace if at all dirty. use good stuff.
Throw in a set of plugs
replace the water pump impeller, and more if needed.

Visually check hoses and such. The little bleed hoses are critical on that engine, as they are the primary lubrication for the mains. Be sure they are in good shape.

hope it helps
John

LU oil is FRESH
Impeller was replaced the day before i bought the boat he showed me the old one and the receipt for the new one...
Primary lubrication for the mail....i mix the oil in the gas no oil injection on this one...dont know if it didnt come with it or if it was removed but i use mixed gas..

 

[j_martin]

Re: RMP questions 115 Mariner

i dont know how heavy the boat is...????

But it's a fishin' bote, not a race bote. (relative)



but this would give me the hole shot and not bog?? but i wont increase my top end?

Assuming the motor will spin it at 5900.


ok so will it hurt to run that prop at 5200 rpm?

No, not at all.



Mixed gas is fine. I don't know if it had a VRO on it. If it did, it was the primitive first try, and mixing in the tank is probably better.

Slow down before you run off and buy another prop.. Check the compression, Get an Oem maintenance manual and fuss with the tuning a bit. Be sure it's running well. Being considerably oversquare (bore vs stroke) there is a fine line between perfect timing and a bomb looking for a place to go off.

Study on motor setup and be sure it's set up right. I suspect it's a little deep.

Ask a lot of questions, pay a little money.

hope it helps
John

 

[davidf5252]

Re: RMP questions 115 Mariner

i dont know how heavy the boat is...????

But it's a fishin' bote, not a race bote. (relative)



but this would give me the hole shot and not bog?? but i wont increase my top end?

Assuming the motor will spin it at 5900.


ok so will it hurt to run that prop at 5200 rpm?

No, not at all.



Mixed gas is fine. I don't know if it had a VRO on it. If it did, it was the primitive first try, and mixing in the tank is probably better.

Slow down before you run off and buy another prop.. Check the compression, Get an Oem maintenance manual and fuss with the tuning a bit. Be sure it's running well. Being considerably oversquare (bore vs stroke) there is a fine line between perfect timing and a bomb looking for a place to go off.

Study on motor setup and be sure it's set up right. I suspect it's a little deep.

Ask a lot of questions, pay a little money.

hope it helps
John

OK will do...

"Being considerably oversquare (bore vs stroke) there is a fine line between perfect timing and a bomb looking for a place to go off. "

i dont know what any of that means...

OH AND I DIDNT MENTION is has a whale tale on it...it was on there when i got which i was told would improve the hole **** but we both know my hole shot sucks....

 

[j_martin]

Re: RMP questions 115 Mariner

OK will do...

"Being considerably oversquare (bore vs stroke) there is a fine line between perfect timing and a bomb looking for a place to go off. "

i dont know what any of that means...

OH AND I DIDNT MENTION is has a whale tale on it...it was on there when i got which i was told would improve the hole **** but we both know my hole shot sucks....

I was wondering how you got out of the hole at all with that prop. The wale tail is a compromise to fix the compromise.

LOL
John

 

[j_martin]

Re: RMP questions 115 Mariner

"Being considerably oversquare (bore vs stroke) there is a fine line between perfect timing and a bomb looking for a place to go off. "

i dont know what any of that means...

Ignition timing a few degrees slow makes it a real dog. A few degrees fast will soon scatter parts all over the lake. It's pretty critical on that engine.

John

 

[davidf5252]

Re: RMP questions 115 Mariner

"Being considerably oversquare (bore vs stroke) there is a fine line between perfect timing and a bomb looking for a place to go off. "

i dont know what any of that means...

Ignition timing a few degrees slow makes it a real dog. A few degrees fast will soon scatter parts all over the lake. It's pretty critical on that engine.

John

how the heck do i check that?? im going to have to pay someone arent I?

 

[j_martin]

Re: RMP questions 115 Mariner

how the heck do i check that?? im going to have to pay someone arent I?

It ain't hard. It's in the book.

When I got my XR4, it was a 55 MPH boat. I was afraid of it at first, but when I got into it, I found a few little things were wrong, timing was wrong, the motor height a little off, Prop was 2 inches too low in pitch, steering was jammed, broken, and out of sync (dual cable). All this was done by a highly paid mechanic that shall go unnamed.

So far it's runing in the low 60's, and I just hauled 3 garbage bags of wet bassboat to the dumpster fixing the boat.

It's the difference between boating indifferent, or driving a well oiled machine.


hope it helps
john

 

[davidf5252]

Re: RMP questions 115 Mariner

It ain't hard. It's in the book.

When I got my XR4, it was a 55 MPH boat. I was afraid of it at first, but when I got into it, I found a few little things were wrong, timing was wrong, the motor height a little off, Prop was 2 inches too low in pitch, steering was jammed, broken, and out of sync (dual cable). All this was done by a highly paid mechanic that shall go unnamed.

So far it's runing in the low 60's, and I just hauled 3 garbage bags of wet bassboat to the dumpster fixing the boat.

It's the difference between boating indifferent, or driving a well oiled machine.


hope it helps
john

nice...ill pick up a manual...

i talked to a really cool guy and he suggested... measure the prop in relation to the pad andmae sure it is 1.5 - 2 inches below the pad.

take the whale tale off and put some new plugs in it and seafoam if i want to....

then see how she does if it is doing the same thing...buy a vented prop...

 

[davidf5252]

Re: RMP questions 115 Mariner

does that sound good to you? of course check the compression, etc.....

but take off the whale tail, new plugs see how she runs and possibly raise the motor on notch?

 

[j_martin]

Re: RMP questions 115 Mariner

That's roughly what I've been telling you for about 20 posts. It isn't quite that simple, though. That prop will run better and better as you raise your engine, right up to the time the engine overheats for lack of cooling water. It's designed to run high.

If you want a reasonable hole shot, and reasonable top end, you're gonna have to change the prop, probably to a vented one. I would recommend the Mercury High Five, pitched for WOT. It'll unload and let the engine go at blast off. When it hooks, it's like riding a sling shot.

The wale tail is probably the only thing that gets the heavy butt of that thing up on the lake (eventually) when the fuel tank and livewells are full.

hope it helps
John

 

[davidf5252]

Re: RMP questions 115 Mariner

Oh I know and I believed you when you told me but it is always nice to call and ask other ppl for different opinions

Well I went home and put new plugs in her and some seafoam....

When at idle for a while and i hit it some times it would bog so bad it would cut off...but when running and then stopping for say 1 minute then hitting it she would jump up GREAT and plane out within seconds...she was spinning 5800 RPM on 2-3 chop consistently

So the only real problem is when at idle for a few minutes no matter what i do she wants to bog and cut off....but after that and she runs i can stop and start and she doesn't do it...

seems as if it is flooding while at idle???? it idles at 800-900 RPMS...

Im still going to check compression and go through it to make sure it is tip top as i dont want to ruin this motor...

Thanks for all your help!!!!