Spent last summer plagued withboat problems that persist

1973delta

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Jun 23, 2009
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Ok so I have a 17ft 1973 Delta Trihull with a Merc 140 I/o. I bought this boat last summer early and had it out 6 or seven times and had a very hard time getting her to plane out. I have tried plenty of stuff but my symptons seem wierd. I am able plane out but only if its me and one other person. I dont have soggy foam or floors as i replaced them all last year. I have a hydrofoil. I replaced the plugs with correct type and gap. new coil. prop is like new with perfect bushing, had it repitched from 17 to 15. I have good compression. I did realize when winterizing that there was no thermostat, which I am now replacing. The outdrive oil that I drained after the season seemed fairly clean not chips or silver color. The boat requires high octane and leaded additive, which I use. Boat idles great no prob. I can get 4300 RPM at WOT but just wont plane with any load. I checked the WOT RPM specs and they say 4200-4600 RPMs. I was about to try and diagnose maybe a fuel problem or point issue, but this should not be a real issue if im getting the rpms. I'm scrathing my head here and dont want to spend another summer putting around at 3 mph on the lake. Also i did notice that the choak body was a little loose when I was winterizing, which I think was causing maybe a slight vacume leak but arent I geting enough rpms to plane out.
 

Bondo

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Re: Spent last summer plagued withboat problems that persist

Ayuh,... Is the bottom of the boat Straight,..?? No hook, No rocker,..??
 

Gary H NC

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Re: Spent last summer plagued withboat problems that persist

At 4300 rpm it should easily be on plane :confused:
 

180shabah

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Re: Spent last summer plagued withboat problems that persist

Are you trimming all the way down/in?
 

1973delta

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Re: Spent last summer plagued withboat problems that persist

bottom looks straight as an arrow. I also have the trim all the way down/in.
 

Bondo

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Re: Spent last summer plagued withboat problems that persist

bottom looks straight as an arrow. I also have the trim all the way down/in.
I can get 4300 RPM at WOT but just wont plane with any load.

Ayuh,... You did leave the trailer in the parking lot,..?? Right,..??
 

Huron Angler

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Re: Spent last summer plagued withboat problems that persist

Will it plane without a load?

Does it sit level in the water?

Could be that you need more weight up in the bow. Sounds like you've already addressed the common culprits here...:confused:
 

1973delta

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Re: Spent last summer plagued withboat problems that persist

Nope. No trailer attached LOL. I'm pretty sure the weight should not be an issue. The foam is dry and wood is clean dry and glassed. I only have a 12 gallon fuel tank in it. It is easier to plane with another person if that person is in front. I just remembered that the Prop tech that re pitched my prop has mentioned that the prop was a little small he thought, this was the prop that came with it so i didn't really think any thing of it, but if you look at the photos that I took you can see that there is a gap that I have not seen on other outdrive to props. In addition, wouldn't I be cavitating if the prop was too small, unless there was another lingering performance issue that has not been addressed? On an unrelated not while I had the camera out I took a picture of a plug that came lose since I have been working on the boat this spring its on the oposite side of the oil vent tube and a little lower. Check out the pictures of the prop and the plug. http://s890.photobucket.com/albums/ac108/thebeerbaron18/
Ignore the pictures of the busted tooth on the Harley transmission, this is another heap of **** that consistently disappoints me LOL
 

SeanMcl

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Apr 3, 2009
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Re: Spent last summer plagued withboat problems that persist

I found this on *another website* (not sure if linking to other places is frowned on here. I know sales are right out!), but it's the top google hit for "mercuiser spun prop". It has some pics, and I've edited some stuff out, so check it out for yourself.

Copied content begins:

Increased RPM With Slower Forward Movement

Many of the emails we receive are related to increased engine RPM and slower forward boat movement. The most cause of this on MerCruiser Pre-Alpha, Alpha One, Generation II and sometimes on Bravo outdrives are as follows :

1st - A spun hub inside of the propeller.
Sometimes the hub will slip inside of the propeller at higher rpm's.

2nd - The incorrect propeller thrust washer.
The propeller thrust washer must match the type of propeller being using. To thick of a washer on a Black Max Prop will not allow the propeller to go deep enough to seal the escaping exhaust gas. The gasses will come out around the propeller instead of going thru the prop causing cavitation. The engines revs up at a certain rpm and slips just like a spun prop hub. Make sure the propeller enters the lower gear housing by at lease a 1/4 of an inch after being torqued down to 50 foot pounds.

3rd - A worn outdrive housing rear inside diameter or outside prop diameter.
If the prop is going a 1/4 of an inch into the lower housing and you still have the same problem, it could be the inside diameter of the lower outdrive housing or outside diameter of the propeller has worn due to getting an anchor rope or something wedged in between the 2 diameters.

4th - A spun engine coupler.
If the propeller appears to be ok and your still having the same problem, it could be the coupler at the back of the engine. Generally speaking, if the rubber hub inside of the engine coupler slips, you should be able to smell burning rubber at the rear of the boat.
 

Bondo

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Re: Spent last summer plagued withboat problems that persist

Check out the pictures of the prop and the plug.

Ayuh,... You got a Prop for a 4" gearcase on a 4, 1/2" gearcase....
That I'm SURE is a Problem...

There's supposed to be a welchplug in that hole, sealing it...

Btw,... Hit the "Enter" key once,+ awhile,...
A few paragraphs make Readin' Easier.....;)
 

Don S

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Re: Spent last summer plagued withboat problems that persist

bottom looks straight as an arrow. I also have the trim all the way down/in.

Then trim it up, you are plowing through the water. You should only use full down till it starts getting on plane then trim up for best attitude and speed. Trim too high and the bow will porpous, just a bit highter and the rpms will go up and the speed down.
Trimmed to low and it will plow. Low speed and low rpm.
 

bigskiohio

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Re: Spent last summer plagued withboat problems that persist

you should be running a 19 pitch prop not a 15
 

1973delta

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Jun 23, 2009
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Re: Spent last summer plagued withboat problems that persist

Ok, so the problem according to the photos is that the prop is too small? I need a 4&1/2" prop instead of a 4" prop right? Im pretty sure i haven't spun anything because my rpm's would be through the roof right? But wouldn't the wrong size prop, or at least one that was causing such ill performance make my RPM super high, especially on a 15 degree 4" prop.

In addition, I have the plug but how do I reinstall it. Do i need a gasket? I could not find any picture of it in the service manual.

Thanks again for all your help so far!
 

1973delta

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Re: Spent last summer plagued withboat problems that persist

Also I have read the tutorial on how to properly get on and stay on plane "Start with trim all the way in then when on plane to increase speed and efficiency trim out slightly to raise the bow up" The problem is that even if its just me and my girlfriend in the boat I still have such a hard time like 25 seconds plus she has to sit in front in the open bow. This shouldn't be necessary with a 140 hp.
 

JustJason

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Re: Spent last summer plagued withboat problems that persist

Bondo hit the nail on the head. You have the wrong prop. You are exhausting over the prop as well as through the hub. When you exhaust over, the prop doesn't see clean water. Go to a Merc dealer and show him what you got, he'll hit the books and pick out a good prop for you.


You also need to remove the drive, check for water in the bellows, check the gimbal bearing, and with that welch plug gone your going to need a new lower shift cable as well, as it now has water in it. Install the new plug with some loctite.
 

1973delta

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Re: Spent last summer plagued withboat problems that persist

Bondo hit the nail on the head. You have the wrong prop. You are exhausting over the prop as well as through the hub. When you exhaust over, the prop doesn't see clean water. Go to a Merc dealer and show him what you got, he'll hit the books and pick out a good prop for you.


You also need to remove the drive, check for water in the bellows, check the gimbal bearing, and with that welch plug gone your going to need a new lower shift cable as well, as it now has water in it. Install the new plug with some loctite.


alright well.... thats good news and terrible news. But Im glad I know where to start.
 
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