1994 115 merc...hauls tail..way out runs my 110 Rude

[SparkieBoat]

I own a 1989 17.5 pro craft bass boat with a 110 rude. she has a 17 pitch prop ss, and tops out loaded at around 40 MPH and about 5700 RPMs.
My dad just got a deal on a 1994 17' pro craft bass boat that has a 1994 Merc 115 Carbbed with a SS prop 21 pitch.
He picked it up for $2K because the owner could not get fire on the bottom cylinder even after replacing the switch box. Dad dropped it off with me and after about 1 hour I finally saw that the bottom 2 wires on the switch box were reversed. took her out for a test run today with 2 of my children.
I would say I had a slightly lighter than normal load, but man I was not ready for the power I experienced, she was a little boggy getting out of the hole, but once the boat got up we took of like a rocket straight to about 5800 RPMs, with a little trim we hit just over 6K RPMs, I was not surprised when I looked down at the speedo reading 53 MPH, I knew we were doing every bit of it.
WOW I can still not believe the speed of this motor.
I have a friend who just purchased a 17.5 stratos bass boat with a 150 Rude 60 degree OIS, he is topping out at about 5500 RPMs and just over 50 MPH, I forgot his pitch but it is a 4 blade SS prop.

Is it ok to run this merc at low 6K RPMs?

it is already boggy coming out the hole with this 21 pitch 3 blade, I would not want to go to a 23 pitch.
All I can say is I may have just been sold on Merc over OMC, I been looking at Yamaha, and own one right now (4 OMCs), I also have a 1989 Merc 150 that has been waiting on the right boat, I have never run it yet, but the boy that owned it said it would fly on his 17.5 aqua sport. I do not doubt it if this 115 is anything like what I can expect.

 

[1nebel0]

Re: 1994 115 merc...hauls tail..way out runs my 110 Rude

Disable the oil injection and premix is the first thing to do...6000 is a bit much for this motor....You can spin the 2.4-2.5 motors past this but these motors were not designed to go that far... I believe 5200 is max suggested... I would take it to 5500 max and use fresh fuel good oil premixed....I understand your concern about stepping up to the 23 as that will cost you the whole shot but bring you in line with rpm;s. There are many props to try for sure.. You can go to a 4 blade that would help with the hole shot however will be slower prop top end depending. There are so many factors that if you can borrow a number of props and do trial runs you will be able to dial in the boat and motor. I have a 19ft tunnel that took many prop attempts before I got it right...What was suggested didn't work and only trial and error produced the results I was looking for..Good Luck...

 

[JB]

Re: 1994 115 merc...hauls tail..way out runs my 110 Rude

Different boat, different rigging and different prop. How is that a fair comparison of the outboards??

 

[SparkieBoat]

Re: 1994 115 merc...hauls tail..way out runs my 110 Rude

all 3 boats are close to the exact same size and hull design and weight, there may be some slight differences but I would assume they are all very close. I know it is not an exact comparison but this merc has really blown me away. I think a 4 blade prop will be the way to go. just looked here...it shows max RPM range to be 5250 that seems pretty low to me. http://www.piranha.com/motor_specs.php?id=2061
maybe some trim tabs are in order.

 

[CharlieB]

Re: 1994 115 merc...hauls tail..way out runs my 110 Rude

Is this an in-line 4 cyl?

A slight bog on acceleration could be caused by slightly lean idle mixture on the top two carbs
AND/OR
a misadjustment of the accelerator pump.

You can download a service manual from the links provided in the first 'sticky post' in this forum.

Also, is your prop alum or SS?

Does it have the 'vent holes' behind the leading edges of the blades? A vented prop greatly improves spool up on acceleration.

Before repropping I would suggest testing again with more realistic load, propping for light loads could lead to over-propping and lugging the engine later. You can always throttle back a little to keep RPM down but you can't reduce load without tossing friends overboard.

 

[SparkieBoat]

Re: 1994 115 merc...hauls tail..way out runs my 110 Rude

load was not too far off, I would say that a full load would only be another 200 LBS or so. I do not think the bogging is the engine, it just seems to take a few seconds to get the boat up out of the water, once boat is up it runs out like crazy. I currently have a 21 pitch 3 blade SS prop, not vented. I will check out the manuals and take a look at the carbs and accelerator pump. I love tinkering. I still think maybe a 4 blade prop and a set of trim tabs would help get boat up faster, I hope that I could got to a 23 or 25 pitch prop without losing much hole shot, My dad will probably pull the kids sking/tubing once in a while, but mostly fishing..I guess he could just keep the 21 pitch in the boat/garage for the few days he would pull skiers. maybe wrap it in some styo foam and put it in the battery compartment and tie it down good.

 

[CharlieB]

Re: 1994 115 merc...hauls tail..way out runs my 110 Rude

Adding a fourth blade will increase the load and reduce WOT RPM, how much depends on the prop design and manufacturer.

A 'vented' prop can make a substantial difference in hole shot!

Maybe try a 3 blade SS 23P VENTED and see how it works, also try a 4 blade SS 21P Vented

Posting these questions in the prop forum is probably a better idea, the guys in there really do know their stuff.

 

[Faztbullet]

Re: 1994 115 merc...hauls tail..way out runs my 110 Rude

WELCOME TO THE DARK SIDE!!!!!!!!!!
Both engines are same displacement but the Mercs a looper and the 110 a crossflow. Get a 115 60? Johnrude and they will run darn near side by side...

 

[SparkieBoat]

Re: 1994 115 merc...hauls tail..way out runs my 110 Rude

I got a 150 1995 60 degree looper, and I have a friend who has a 1993, I cannot say that I am real impressed..maybe they are just not set up well or something. my friend has his on a 19' stratos bass boat (I thought it was a 17.5 but he corrected me). this 115 will outrun his once I get it propped right. it will keep up with his now. even though his boat is 19' it is really not that much bigger or heavier than my 17.5, it appears to just have a longer nose