Drastic drop in pitch needed?

[MrEye]

I am running a 1992 Merc 60hp 2-stroke on a 17' Lund Pro-V tiller. Bought it last year and it had 2 props. One 17p and one 16p. Right away I new that the boat was pitched wrong. The motor was turning about 4200 WOT with the 16 on it. It is rated to turn 5000-5500rpm. I dropped to a 13p and the power did get better bit the rpm only increased to 4400. I have not checked compression yet but the motor runs and sounds perfect. I inquired at a dealer on dropping to a 10p and he said that I was so low in the rpm's to just go to a 9p. Either would probably work but since props are basically non-returnable I want this one to put me in the right rpm range. Thanks for any information.

 

[Scott Danforth]

I would suspect an issue with the motor itself. What are the results of the compression test?

 

[MrEye]

As I stated I have not run a compression test. Would there be other symptoms of low compression? The motor starts and runs like a top.

 

[Mi duckdown]

check compression first, then go from there. it cost nothing to check that

 

[Scott Danforth]

Im going with either low compression or a fuel system issue. with a 13p you should have been hitting 6000+ RPM easy unless you have a long shaft motor on a short shaft transom.

 

[steelespike]

I suspect the tach is off what is the gps speed at 4200 16" pitch and at 4400 13" pitch?

 

[MrEye]

Thanks guys. Guess I was suspecting something like that. I will have the compression checked and as soon as the ice is off get a speed also. What would be considered "Low" numbers for the compression?

 

[steelespike]

Ideal minimum is considered to be 100 psi. and within 10% between cylinders.
Is the hole shot strong?Does it start easily and idle smooth and evenly?

 

[Sea Rider]

After checking compression run half a can of Power Tuner through carbs, follow can instructions, does wonders to 2 strokes engines. Is your engine well trimmed, boat with weight well distributed on deck. Does engine sits at the sweet transom height ?

Happy Boating

 

[Maclin]

What altitude do you boat at?

 

[MrEye]

Wow love the feedback. To answer some questions: I am at 1500ft altitude. The boat is a 17' Lund. Battery front and back, Pretty normal fishing boat set up. The motor has power trim and it trims the boat out well. The hole shot is what I noticed first. The 60hp should have more than that I thought. With 3 people in the boat will barely get up on plane even with moving the weight to the front.The motor starts and runs excellent. No smoke and no miss or rough idling. I will check compression 1st I guess and rule that out.

Thanks again to all.

 

[Frank Acampora]

I never heard of a 60 on a planning hull using a 9 pitch prop. I hate to say it but based on my experience in selling a 60 for use on a 17 foot LUND, you simply may not have enough horsepower. The guy was MUCH happier with a 90--even though it was above the horsepower rating. I sold him the 90 but refused to mount it. That was his problem if he was caught.

 

[Maclin]

At 1500' then altitude is not a factor. By way of comparison, I had a 15.5' Fiberglass TriHull with a 55hp. A 12 pitch was a little too much and would tend to lug with more than just me in it. A a 10.5 was not enough, would it would try to overrev no matter the load and top speed was just not there. An 11 was just right.

 

[MrEye]

I never heard of a 60 on a planning hull using a 9 pitch prop. I hate to say it but based on my experience in selling a 60 for use on a 17 foot LUND, you simply may not have enough horsepower. The guy was MUCH happier with a 90--even though it was above the horsepower rating. I sold him the 90 but refused to mount it. That was his problem if he was caught.

I tend to agree that the boat could handle more hp but being a tiller model, it is rated for the 60 and that's it. Way too many checks here to try to get around that one. But even at that the motor should turn more rpm. Plan is to start with the compression, then maybe onto the fuel pump and filters. I have also heard that it could be a timing advancement issue? Gotta warm up here a bit though, still 2' of ice.

 

[dazk14]

A 60hp is fine for that rig. Everyone wants more power, but with good prop selection it'll be a very serviceable rig.

What are the current top speed numbers?

Did you say it is still a dog out of the hole with the 13" pitch prop, but trims out fine once on plane. I'm presuming you're tucking in(trimming down) the motor while trying to plane.

 

[MrEye]

A 60hp is fine for that rig. Everyone wants more power, but with good prop selection it'll be a very serviceable rig.

What are the current top speed numbers?

Did you say it is still a dog out of the hole with the 13" pitch prop, but trims out fine once on plane. I'm presuming you're tucking in(trimming down) the motor while trying to plane.

Sorry I do not know the speed. I will certainly get it though once the lakes open up around here. I am tucking the motor under as far as it will go to get the boat up and backing it out once up on plane. The trim is very affective. I should also mention that I added a Hydro Foil to it to help. The hole shot did improve with the 13p prop and not that I have 3 people in the boat very often but it is also better with that but far from right. The closest thing that I have had to this was a 70hp Yamaha on a much heavier fiberglass boat. The low rpm's is looking like the issue. I will certainly post the compression numbers and speed once I get them. Obviously hoping for something simple like a fuel pump or wot timing issue.

 

[steelespike]

A foil can work fairly well on some setups.But on the wrong setup it can handle oddly and lose top speed.
Get the top speed and rpm with the foil and without. Actual hole shot time with both setups.

 

[MrEye]

Ya, I didn't notice too much with the foil. If I did notice anything the steering pull was a bit stronger when trimmed out. Nothing all that noticeable though. I think that when I find that missing 1k rpm it will be like having a new rig.

 

[MrEye]

Ok, finally was able to get something done.
A: compression was 130 range all 3 cylinders
B: timing good and advancing
C: Dropped lower unit to check exhaust ports - clean
D: carbs all working properly

In a nut shell could not find anything wrong.
In talking with a local Merc dealer he also noted that the 17' Lund Pro-V in a lot of boat for a 60hp. Nothing I can do about that legally. He had a guy in last year with the exact problem. A 60hp on a very similar Lowe Boat. They ended up with a 9 pitch Merc prop.
He just happened to have a used rebuilt 9 pitch that he offered me to try.

Wa-la, the boat takes off like a rocket. As far as the engine performance goes it is now turning 5200 rpm on the tach and pushing the boat at 29 mph.
I ended up taking the foil off because the boat actually handles and corners better without it. Removing it did not change the rpm's or mph either way.

 

[SkiDad]

Interesting... nice result !

seems after looking the 1992 has a 1.64 gear ratio - I guess that explains have to go so low on pitch