Which prop should I be running on Johnson?

N

northface owner

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Jul 2, 2005
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Hello everyone! I have been having trouble with speed/rpm's on my pontoon, and hope you experts can help me.<br /><br />I have a 1989 Misty Harbor pontoon boat (the one with large square pontoons with inverted V on bottom), it is a fairly heavy boat and I dont know how much it weighs, or even if that is important.<br /><br />I have a 1973 Johnson 135 HP motor that we bought seperately and installed on this boat. Since the motor already had a prop on it we went ahead and used it. The prop is a 13 X 19, and not in the best shape. I did remove it and sharpen the edges, which seamed to help some. It does have a dime-size chunk missing from one blade. <br /><br />The engine tag says it should run between 5000-5500 RPM at WOT, but the tach on the dash is only showing 4200 RPM's. We can lumber around the lake at a whopping 18 MPH, and thats not good enough. We used to have a 135 Evinrude on this boat, and I could ski behind it, now we can barely go tubing. When I make a turn the boat slows down tremendously, which is to say it DRINKS fuel. Also, at times when I make a turn it seams as though the prop stops spinning altogether, and when I let up on the throttle it will take off again.<br /><br />I need this boat to do these things:<br />a) go faster<br />b) be more efficient<br /><br />Can anyone help?<br /><br />Thanks in advance!!!!!
 
P

paperdesk

Petty Officer 1st Class
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Mar 28, 2004
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204
Re: Which prop should I be running on Johnson?

Welcome northface! I have the same motor (the Evinrude versions). The 73' johnson and evinrude are the same motor, just marketed under a different name.<br /><br />Can you take the prop off your old motor and slap it on the new one and see if it does any better? Do you know what size your previous prop was? Do you have this motor mounted and adjusted the same as the old one?<br /><br />Hope you get it going! I'm no expert so hopefully one of the old timers will happen by and give you some solid advice.
 
N

northface owner

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Re: Which prop should I be running on Johnson?

I do wish I still had the old motor, that would simplify things a bit. I sold the old one a few years back, so thats not an option.<br /><br />I am hoping an "ol timer" will be able to kick in some advise. I did find some useful infor at the following link: http://www.boat-props.com/info/prop_info.cgi?page=rpm <br /><br />It did shed some light on the subject, but some free advise from a pro would be even better.
 
Barnacle_Bill

Barnacle_Bill

Admiral
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Feb 8, 2004
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6,469
Re: Which prop should I be running on Johnson?

Ted is right, what size prop was on your old motor. With a chunk missing out of one blade, the prop is out of balance. There is a good chance it hit something and possibly spun the hub. This would also explain the problems you have in turns. If the motor came off lighter boat you may need to drop down to maybe a 15 pitch to get your rpms up. Perhaps you can borrow a good prop and then give us some figures. Hopefully someone else has a similar rig and can give you a starting point for the proper prop. Meanwhile, I wouldn't be runing that at WOT with that prop or you may wind up with a lot more expensive repairs due to vibrations.
 
J

jason389

Cadet
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May 15, 2005
Messages
27
Re: Which prop should I be running on Johnson?

Hey northface, it definitely sounds like you have too much pitch for your rig. And even a small chunk out of a blade it too much, out of balance like ibfishn said. The motor maxing out at 4200 rpms means (most likely) that the motor can't turn the prop, too much pitch. (like tires that are too tall on a 4X4). Definitely check the hub too. You might try a 15, 16, or 17 pitch. You want to find the sweet spot between holeshot and top end power. The hustler 2 piece prop is a good cheap alternative, I have bought them and had good luck. You can buy 1 hub and then change just the blade (prop). If you got, say, a 15 and a 17, you could change the prop out depending on your load and or what you want to do that day (fish, ski, haul butt). Hope that helps.
 
N

northface owner

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Jul 2, 2005
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Re: Which prop should I be running on Johnson?

Thanks guys! I am going to mark the hub/prop and see if the marks line up after I try to run it again. This should tell me if the hub is spun.<br /><br />It does make sense that with the chunk missing, it would be out of balance. I should keep this old hub as a backup incase the new one I install ever fails (just to get back to shore). <br /><br />Is there any reason this large of a boat should not perform better due to its size and weight? I realize it will only do so much, but I feel it should do alot more than it is right now.
 
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