15 Hp Johnson won't plane 12 foot boat.

[JamesMiller]

I have a 95 15 h.p. Johnson (J15EEDS) model # G 04072438 engine that has approximately 17-18 hrs. with a new carburetor installed that will not rev up to full throttle until boat planes-out which takes a unusaully long time. Carburetor is fresh from johnson because I tried to play mechanic and ruined metering rod. There is one needle valve on the whole carburetor and it seems to have no effect on whether the engine will reach WOT. any suggestions??

 

[ob]

Re: 15 Hp Johnson won't plane 12 foot boat.

What pitch prop are you running?

 

[JamesMiller]

Re: 15 Hp Johnson won't plane 12 foot boat.

factory prop is installed on this outboard. I double checked. It should go WOT with the boat in drive and sitting still, maybe the spark advance is off?? Made discovery that needle valve is for idle mixture only.

 

[ob]

Re: 15 Hp Johnson won't plane 12 foot boat.

In your first post you imply that the engine gets to WOT after an unusually long time.Engine could be mounted too low on tansom or you are overpropped.Don't know two things .Overall weight of boat ,persons,& gear and what is the pitch of the prop you are currently running?<br /><br />They make from 10"X 5" dia & pitch to 9" X 11".Impossible to make recommendation without more info.Did boat ever run well with current motor and prop?I don't know.If so,we can begin chasing another problem.

 

[Solittle]

Re: 15 Hp Johnson won't plane 12 foot boat.

James - Also check the transom angle adjustment of the motor and the distribution of the load in the boat.

 

[JamesMiller]

Re: 15 Hp Johnson won't plane 12 foot boat.

the prop numbers are 9.5*12.5, does that help?? This engine-boat combination was my Grandfather's before he passed away, I do not know how it ran on the water prior to my obtaining it. The boat probably weighs about 200 lbs. gas tank holds 3.5 gallons and I weigh 250 lbs. I moved gas tank forward and that helped, boat won't plane out if I don't shift my own weight forward. Engine is all the way forward with the bottom hole pinned.. when I start moving it back the nose of the boat comes up and it will not plane at all. The engine cannot be moved up any higher on the transom, it is flat across the top. <br /><br />Let me say this again.. The engine will not rev to full throttle until the boat planes out, it should rev to WOT with this prop, right?? I am told that this engine should "stand this boat on it's *** ".

 

[JamesMiller]

Re: 15 Hp Johnson won't plane 12 foot boat.

also forgot to add.. have changed spark plugs and the engine runs like a top, no spitting or sputtering or any hesitation.. it just won't go WOT until the boat planes off. that prop was actually 9.5 X 12.5 not 9.5*12.5,.. Also, I would like to thanks you guys for taking the time to help me with this maybe I can help someone else, too. James A. Miller

 

[ob]

Re: 15 Hp Johnson won't plane 12 foot boat.

I'd try dropping back to a 9" X 11" prop and water test.You can visit a prop shop and I'll bet that they will let you trial a new or used one.

 

[BF]

Re: 15 Hp Johnson won't plane 12 foot boat.

I'd guess it's something other than the prop pitch. I've got a 15 hp on a 16 aluminum, and with me, light fishing gear, full tank of gas (5 gal) and waggy-tailed labrador (total ~550 lbs), that motor is great. Pops up on plane and does >20 mph. My prop is 9 X 10. A lower pitch would help when I've got a bunch of folks in the boat. <br /><br />With a 12' and just one person, I'd think you should be flying!! Check to see that the throttle linkage is free throughout it's range.<br /><br />good luck.<br /><br />Brent

 

[OBJ]

Re: 15 Hp Johnson won't plane 12 foot boat.

James....this may be way off base here but....<br /><br />were does the anit-cavitation plate set in relationship to the keel of the boat? I'm talking about the plate right over the prop.<br /><br />The anti-cav plate should set (just a rule of thumb here) equal to or no more than one inch above or below the keel.<br /><br />If your boat has a 16" transom, the engine should be a short shaft. You could even get by with a 17" transom with a short shaft. Anything more would require a long shaft. A long shaft on a boat needing a short shaft would greatly decrease the performance of the engine.<br /><br />Don't know what ya' got...just asking questions.

 

[chilifriedpork]

Re: 15 Hp Johnson won't plane 12 foot boat.

Why was a new carb installed?<br /><br />There must be something seriously wrong here. I have a 15hp on a 12ft and I can't control the **** thing at full throttle.<br /><br />Make sure the jetting in the carb is stock. Even if it was a 9.9 carb, it would easily plane your boat with 2 ppl aboard. If you have time, go through the intake and exhaust passages and make sure the passages aren't blocked. (ex. carbon, broken reeds)<br />-make sure the tiller arm->carb linkage opens the butterfly valve fully, and that the jetts are clear.<br /><br />Just make sure the boat is trimmed correctly to optimize this engies performance.<br /><br />Good luck!

 

[Boatist]

Re: 15 Hp Johnson won't plane 12 foot boat.

James<br />I think you have way too much pitch in your prop. The standard prop is 9.5 by 10 by 3 blade.<br />I have 3 props for my 1975 15 hp on a 14 foot aluminum boat. With two lite people 150 lb or less and light fishing tackle it will plane. With 3 or heavy tackle it will not plane. My boat is 167 Lbs. This is with the standard prop of 9.5 by 10 and used for 12 to 14 foot aluminum boats. You are trying to start and get on plane in a very gear.

 

[Jack Shellac]

Re: 15 Hp Johnson won't plane 12 foot boat.

I'll have to agree with Boatist. My 15 HP Johnson with a 9 1/2 x 10 prop planes off a heavy 14' wood boat with no problem. That's with two people and a six gallon tank in the boat.

 

[dakotashooter2]

Re: 15 Hp Johnson won't plane 12 foot boat.

A 15 HP motor + 6 gal. tank + 250 lB person all in the back is a lot of weight in a 12 ft. boat. Too much to balance the boat. I only weight 140 and with a 9.5 and 3 gal tank I have to use ballast in the front of my shallow 12' boat if I want it to plane quickly. A couple others made similar comparisons but also mentioned a passenger who generally sits in the center or front and that helps to balance the boat or larger heavier boats. My brother had a 12 with a 15 and had the same problem when he was alone. Remember that small boats are much more sensitive to weight distribution than larger ones.It may be one of the other problems mentioned or a combination of, but I think your biggest problem is the weight distribution.

 

[lbi14lbb]

Re: 15 Hp Johnson won't plane 12 foot boat.

The prop you have was designed primarily for 1993 15 hp Johnson according to Advantage Prop website. It's part number is OMC 175323 and is unique in pitch and diameter to the 15 hp for that year. Why, I have no idea. I have the '93 Johnson and its on a 12' Carolina Skiff, center console. Weight distribution is a problem when I'm alone but with someone sitting upfront getting on plane is easy and she flies.<br /><br />Hope this helps.

 

[JamesMiller]

Re: 15 Hp Johnson won't plane 12 foot boat.

O.K guys, I have read all of your posts and my friend finally went with me yesterday on the river. He tells me that the carburetor probably needs a bigger jet. The jet is from the factory, I just bolted it on and went for a ride! I had to adjust the linkage so that the butterfly wood open up flat but that made no difference, it's like it will only rev so far. Just don't get it.

 

[JamesMiller]

Re: 15 Hp Johnson won't plane 12 foot boat.

I think I will get a 9.5 X 10 prop for this machine and see what happens.. folks, you couldn't ask for a better running engine, I am a mechanic, just not an outboard mechanic!!

 

[chilifriedpork]

Re: 15 Hp Johnson won't plane 12 foot boat.

And if the prop don't fix it, then try the jetts

 

[Boatist]

Re: 15 Hp Johnson won't plane 12 foot boat.

James <br />I do not think it will be a jet problem. All 15 use same jet unless you are at high altitude, and then you use a smaller jet. Are you sure you got the carb for a 15 hp and not a 9.9 hp?<br />I think when you put the right prop on you will see a big difference.

 

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