115 mercury

[huntercj]

I bought a used 17 foot lund ss with a 2008 115 four stroke mercury out board on it. I was talking with a coworker and he bought a brand new 17 lund ipact with same motor and same prop as mine he says his runs 42 mph 5800. My boat only runs 4800 rpm about 35 mph just wondering if some thing could be wrong. prop pitch is 17 on both boats.

[Kyhl]

I think you are onto something. Doesn't sound right to me.

My first thought would be to remove the cowling and work the throttle with the engine off to verify that you are getting to full throttle.

On a second note, I'm surprised neither of them are not running higher than 6,000 rpm. Are you sure they are 17's? Are these aluminum props?

I have a Merc 115 4s on an 18' Alumacraft and a 17" pitch aluminum hit my rev limiter at 6,500 rpm. It probably would have kept spinning right up to 7k. I now have a double cupped stainless 17P and it will run 6,200 with a light load running with the wind.

My point is, I'm surprised that a 17' boat with a 115 4S and a 17" prop would run less rpm. Maybe they changed gear ratios between 2004 and 2008.

I agree with you. Something doesn't sound right.

[BartmanMN]

I don't know the difference between my Optimax 135 and the four strokes, however I had a similar issue and ended up needed to replace one of the injectors. Motor ran fine all the way to WOT, then it would hesitate a little bit and not go to full RPM's.

Just throwing that out there. Mechanic can hook the computer to the motor and make all injectors click one by one. You could tell that I had a bad one with that test.

[delcecchi]

I bought a used 17 foot lund ss with a 2008 115 four stroke mercury out board on it. I was talking with a coworker and he bought a brand new 17 lund ipact with same motor and same prop as mine he says his runs 42 mph 5800. My boat only runs 4800 rpm about 35 mph just wondering if some thing could be wrong. prop pitch is 17 on both boats.

How thoroughly did you have the motor checked out before you bought it? 4800 rpm is way low. You ought to be getting around 40 mph with that boat and motor, at least.

Might be a good idea to take it somewhere and get it checked out. Is it still under warrantee?

[17FishMan]

Yes you definetly have something wrong with that motor. Running a 17 pitch aluminum on that boat should easily get you to the rev limiter. I have the exact same motor on a 2008 1750 fisherman with 16 pitch Vengence SS and I get 42 mph @ 6200.

You have a smaller and lighter boat so you should easily get to the mid 40s at your rev limiter. Are you sure that you are getting the trim set correctly? If you leave the motor all the way down you would get these type of numbers.

[huntercj]

I had the motor scaned to check the hours on it i when i bought it. I did some checking it has the orginal prop on it and acording to the scan it use to run up to 6250 rpm so some thing is not right. Anybody no of any good dealers i live in the roseau area and i am willing to haul it with in a couple of hours of here . Called a couple of dealers they say just change prop thats not going to fix whats wrong with it. The motor has mercurys 5 year waranty on it not sure what it will cover or if its transferable.

[fishhuntwork]

I have a 2009 crestliner superhawk 1700 with a 4 strork 115 mercury. I just actually ordered a new prop from prop md. We ordered the new mercury 4 blade alum. the pitch is a 15. I was running about 5400 rpms and about 35 mphs with my 19 pitch. I will let you know how that goes when I put it on. I may have to go to a 17 pitch but will soon find out.

[delcecchi]

You went from a 19 to a 15? Why?

[reinhard1]

i've got a 115 Merc 4stroke and i've had a 15 on there since i bought it. trolls good and got plenty of speed for me. good luck.

[fishhuntwork]

I was trying to get overall better handling and closest to max rpms as I could. I've heard good things about prop md and he did the figuring for me.

[Kyhl]

The 19 to 15 wasn't a straight 3 blade to 3 blade switch.

I ran into that too going from a 19 to 17. Within three blades of the same model from the same manufacturer. They dropped the diameter 3/8 of an inch which caused me to double cup the 17.

In his case, hes going from 3 blade to 4 blade so who knows what will happen. Props are crazy.

[marine_man]

What does your tach show your motor is idling at?

It's possible your Tach is off, or on the wrong pole setting, but I would have thought the prior owner would have caught on to that.

Does it seem like it's running at full speed, or does it seem like it's bogging down?

marine_man

[WARRIOR 2090]

that motor should run 6400 rpms before you haul it too far I would try a set of plugs in it it would be a cheap fix before dragging it to far to get it looked at otherwise I am a certified merc.tech call me and we can talk about it 2one8 6nine2 thirtysevenfiftytwo these motors are built off of the varedo block so they are over built and very derable we run seven of them in our rental fleet and they have been tough motors

[fishhuntwork]

I installed my new prop, wow what a difference. It planes fast, increased speed by 7 mph, and runs at 6200 rpms. I wish I would have done this long ago.