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Repowering Super Sport 15
sailorman	#1  Posted on 10/26/15 - 12:36 PM
Member Posts: 35 Comments: 0 Joined: 01/12/15	I am on the fence between a Yahama 60 and the newer F70. It seems like 60 hp should be plenty of power but the dealer is really pushing the newer 70. The price difference is about $600. I will be pulling grandkids on a tube and it will not be unusual to have 4 people in the boat. I have a 2001 50hp Johnson now and it runs great with just one aboard but really struggles with a load only reaching 3500 RPMs when loaded. Any suggestions would be appreciated. My 1985 SS15 is in great shape always stored indoors. I just finished replacing all of the mahogany and rechroming some parts. I hope to keep it for a good while and my grandkids (12 years old) will be using it soon on their own. I am a bit concerned that the 70 will be to much for them. Thanks
Joe Kriz	#2  Posted on 10/26/15 - 12:41 PM
Site Owner Personal Page Personal Album Photo Albums Project Albums Posts: 11433 Comments: 452 Joined: 03/18/05	I would look into having the throttle stop adjusted so they can't get to full power. There is usually a screw on the motor for that but not sure about the newer models. Other then that, I would go for the 70hp so when they get older, you could adjust that screw to give them full power if they need it.
Phil T	#3  Posted on 10/26/15 - 12:45 PM
Administrator Personal Page Personal Album Project Albums Posts: 6989 Comments: 6 Joined: 03/26/05	I have a 2001 50hp Johnson now and it runs great with just one aboard but really struggles with a load You should get a second prop that is sized for the load. Cheaper than a new motor.
sailorman	#4  Posted on 10/26/15 - 12:53 PM
Member Posts: 35 Comments: 0 Joined: 01/12/15	A new prop would be a lot cheaper. What would that do to my speed? top speed now is 29MPH with just one aboard.
Phil T	#5  Posted on 10/26/15 - 1:59 PM
Administrator Personal Page Personal Album Project Albums Posts: 6989 Comments: 6 Joined: 03/26/05	With a full load, I would guess 24 mph assuming clean or smooth painted bottom, engine at correct height and weight balanced out.
sailorman	#6  Posted on 10/26/15 - 2:04 PM
Member Posts: 35 Comments: 0 Joined: 01/12/15	Thanks for the speed estimate. I have been reading about another Whaler 15 owner who went to the F70 and he seems really happy. It is just a pretty big amount of money to have tied up in a boat I just bought this spring for $5,000. The F70 rigged is going to be $9,250.
tedious	#7  Posted on 10/27/15 - 6:51 AM
Member Personal Page Posts: 1072 Comments: 2 Joined: 09/07/08	Sailor, I have a 1989 SuperSport 15. I put an F70 on it the first year they came out, in 2010 (it may be newer than the F60, but it's not really new). I love the F70, especially since I finally found the right prop to run on it. I can't compare to the F60, as I have never run one. I feel your pain regarding putting a motor on that eclipses the cost of the boat - pretty much everyone who repowers has that concern. It does not make sense if you look only at economics, but I can tell you the F70 is a wonderful motor - very reliable, quiet as can be, easy to work on so if you are going to be keeping the boat a long time, it's a good choice. The F60 would have those same characteristics. The price you were quoted seems quite reasonable; the $600 bump over the F60 is pretty minimal in the grand scheme of things, and is less than the typical $100/hp. Regarding the grandkids running the boat, the 15 is a fast, bouncy, agile boat - a real sports car on the water. They'd easily be able to get into trouble with either the F60 or the F70, or really any motor. If you do go with some type of throttle stop, don't install it until you get to about 50 hours on the motor - Yamaha 4-strokes are best run hard during breakin to seat the rings. Good luck! Please feel free to ask any additional questions you have. Tim Edited by tedious on 10/27/15 - 6:56 AM
wlagarde	#8  Posted on 10/27/15 - 7:04 AM
Member Personal Page Project Albums Posts: 442 Comments: 2 Joined: 07/21/13	Sailorman - I'm surprised your performace is so poor with your 50 but perhaps its because your motor is old and not producing 50hp anymore. I have a 2005 50hp Nissan and I'm seeing ~34mph with a heavy load (3 young children and 2 adults + fuel and gear) and 38mph with a light load (me + gear). If you get the 60 it will be plenty of power but if it were me I would get the 70 given such a small price differential. 1976 Sport 15 w/ 2005 50hp Nissan 2 stroke
tedious	#9  Posted on 10/27/15 - 7:17 AM
Member Personal Page Posts: 1072 Comments: 2 Joined: 09/07/08	Rereading your original post: you mention sluggish performance when loaded, and being unable to get more than 3500 RPM. You also mention a maximum speed of 29 MPH when running light. What RPM are you reaching when you hit that 29 MPH? You may be able to improve things significantly by simply changing the prop. Also, at what height is your motor mounted? That is, what set of holes on the motor are the bolts in? Many motors are mounted too low, which also affects performance. Tim
sailorman	#10  Posted on 10/27/15 - 10:13 AM
Member Posts: 35 Comments: 0 Joined: 01/12/15	She runs at 5200 when she is running light and things are going well, then sometimes she will start to run a bit rough and not go over 3500. At 5200 she is running 29 MPH. The engine is not mounted as high as some I have seen on this site. The top lip of the mounting bracket sits right on the transom top. It looks like the lower holes in the bracket don't have but one place to go maybe the guy who installed this motor drilled his own holes in the bracket. The upper holes can allow it to be raised a couple of inches but then the lower bolts would need to be redrilled to meet any other holes. By the way, thanks to you guys who have answered, I appreciate your help and advise.
tedious	#11  Posted on 10/27/15 - 10:25 AM
Member Personal Page Posts: 1072 Comments: 2 Joined: 09/07/08	Sounds like your motor is mounted using OMC's "blind holes" - see a description in the Rigging folder of the articles section at this site. The blind holes rig the motor "all the way down" which is not optimal. You could improve the performance of your current motor by rigging it 2 or 3 holes up. 5200 RPM is not horrible, but you really should be up around 6000 when running light, so you are overpropped by a couple of inches of pitch at least. That is contributing significantly to your poor performance when loaded. So if you feel like trying to make it better, as opposed to getting a new motor, you can move your current motor up, and then try a different prop. It will make quite a difference, and cost a lot less than an F60 or 70. On the other hand, it will still be an old-tech 2-stroke, so it's going to be quite noisy, smelly, and thirsty compared to a modern motor. Tim
MG56	#12  Posted on 10/27/15 - 11:16 AM
Member Personal Page Posts: 355 Comments: 0 Joined: 05/11/13	Sailorman, a couple people have mentioned the possibility of making your Yammy 50 run right. Is that something you are open to? Because I think a 50 hp works for what you want right now, and if the engine is clean & you trust it I think it is worth exploring. A lot of things come into play, like bottom paint, engine height & prop. But I will bet you that doing a proper de-carb on that engine will put a smile on your face. I see this all the time when someone buys a nice clean old boat, the engine runs rough or doesn't perform, etc. Well the very fact that these old boats haven't been used is why the engines don't run right. Engines like to run and every time you randomly run them just means another layer of varnish builds up. Putting a bottle of magic into the gas tank isn't a proper de-carb, it is a specific procedure to remove the build up. The additive you use needs time to work so you have to allow it to. Initially you will blow a mound of gunk out of the engine, but you aren't done and have to cycle that solvent rich fuel mixture through the engine many times and let it sit. If you like how the engine runs a new prop is a good investment.
sailorman	#13  Posted on 10/27/15 - 3:05 PM
Member Posts: 35 Comments: 0 Joined: 01/12/15	I do like the idea of this Johnson 50 and I like the way it looks on my boat. Are you suggesting that I should add an additive and decarb the engine. It sounds like there is more to it than that. How much actual performance benefit is raising the engine two holes? I will need to remove the lower bolts, reglass the holes and redrill holes that will match up with the lower holes on the engine bracket. I can do that if you guys think that it will really makes a difference. A new prop is certainly in the mix. I just don't want to do all these steps and spend another $500 or $600 just to buy a new Yahama F70 anyway. I know it's my call but I really appreciate your advice as you own these boats too and I value your opinion. Thanks
Joe Kriz	#14  Posted on 10/27/15 - 4:22 PM
Site Owner Personal Page Personal Album Photo Albums Project Albums Posts: 11433 Comments: 452 Joined: 03/18/05	Here is wlgarde's project where he drilled the "Green" holes in his 1976 Sport 15'. http://www.whalercentral.com/userphot...lbum_id=64 You want to drill the lowest holes you can in your transom. The Red is standard if your 1985 can be drilled using them. If not see if the Yellow holes will work. If not, then the Green will for sure. Measure the new holes twice inside and out before drilling.
WRufus	#15  Posted on 10/27/15 - 6:30 PM
Member Personal Page Posts: 73 Comments: 1 Joined: 01/15/13	I'll also say the F70 is an incredible motor. Super reliable, starts instantly, very quiet, sips fuel - you can run all day hard on 5 gallons or less. But that's a whole lotta motor for a 15 - It would scream. If you don't want that, a throttle reducer is a good suggestion. I am told by my master yamaha mechanic, that outboard hp used to be measured at the powerhead vs now it is measured at the prop. Thus older hulls are getting more hp at the prop when you are running the max outboard hp rating with a new motor. I am not sure the real difference and end result, but it is an interesting fact. It would be cool if yamaha had a new & light 100hp outboard - Because I would like to see how it would push a 17 hull! 1989 Montauk 17' w/ F70 Yamaha
tedious	#16  Posted on 10/28/15 - 2:10 AM
Member Personal Page Posts: 1072 Comments: 2 Joined: 09/07/08	Sailor, it's obviously your decision, but if you generally like your Johnson 50, making an effort to get it working properly would seem to make sense. It's not a sure thing that you'll be able to get it working, but if you can, you save a ton of money. You're looking at 3 steps: 1) Fix whatever is wrong with your motor. While a decarb won't hurt anything, it sounds to me that it may be time to rebuild the carbs. This is not a huge deal - many consider it to be a routine maintenance item that you need to do every few years. If you are handy, you can get the factory service manual and tackle it yourself, otherwise it will be several hundred dollars for a mechanic to do it. The parts are about $35 per carb. 2) Lift the motor. I had a Johnson 70 on my 15 before I got the F70. The motor was all the way down when I bought it, and I ended up raising it two holes. It was not a massive difference in top speed, but the Johnson 70 had power to spare - my guess is it would make more difference with your 50. Raising the motor did significantly improve the handling - lightened up the steering quite a bit. You can do this job yourself, if you are so inclined. Also note that if you end up going with the F70, you'll need to do this job anyway as the F70 cannot be mounted with the blind holes. 3) Get a new prop - this may or may not be needed depending on the results of 1 & 2. You have not specified what prop you have on there now, but assuming you don't have one already, a good quality, modern, stainless steel prop will really make the boat come alive. It may take a couple of tries to find the perfect one for your situation, but if you are looking to keep the boat for a long time, it's worth it. So my recommendation would be to do 1 & 2, and wait and see on #3. For reference, the switch from powerhead rating to prop rating occurred in 1986, well in advance of the manufacturing date of your motor. Tim Edited by tedious on 10/28/15 - 2:21 AM
sailorman	#17  Posted on 10/28/15 - 12:26 PM
Member Posts: 35 Comments: 0 Joined: 01/12/15	I had the carbs rebuilt this spring when I bought the boat. I just dropped her off at a good mechanic's shop to have him check things out more thoroughly he thinks perhaps she needs a new power pack. I'll let you know what I find. I am going to see what the prop size is so that I can bounce it off you guys who may know if it's wrong. The new engine vs. old is like fire and ice. It's all I think about. Caroom, what prop size did you finally settle on on your new F70. I will make the call when I hear from the mechanic. Thanks again
TookyAndNatasha19	#18  Posted on 10/28/15 - 11:45 PM
Member Posts: 23 Comments: 1 Joined: 09/27/15	sailorman, Both the Yamaha F60 or F70 will make an old Sport 15 scream. The main difference between the two motors will be the larger one will out hole shot the smaller one, and the smaller one will be a little slower on the top end than the larger one. If you are going to be carrying a load where the hull is at full capacity at all times, you might want to opt for the F70. It will handle the load easier. The old Johnson might not be the best thing to continue to throw money out. I have the same boat, and after doing many things to my old Johnson 70, I finally sold it. I still have not repowered our Sport 15 yet, but when I do, it will be the Yamaha F70.
tedious	#19  Posted on 10/29/15 - 5:03 AM
Member Personal Page Posts: 1072 Comments: 2 Joined: 09/07/08	It's certainly a good idea to rebuild the carbs, as you did, when you buy an older motor with an unknown service history. That does not rule out a carb problem now, but it makes it a lot less likely. It will be interesting to see what the mechanic comes up with. With my F70 it took me 4 tries to find the right prop. I tried the Stiletto Advantage 1 in both 13 and 15-pitch, and the Stiletto Star in 15-pitch. I settled on a 16-pitch PowerTech SCD-3 - with less blade area, it seems to be a much better match for the peaky F70 than the large, grippy Stilettos. Depending on how fast your 15 is, and with what loads you typically run, you may want a 17 or even an 18 pitch in the SCD3. Running alone, I can hit the rev limiter if I trim out enough. I typically can't go that fast in the conditions I am in, so the 16 is perfect - lets me hit close to 40 with only a tiny bit of trim, and acceleration is very strong. One other prop to mention is the Turbo Quest - they advertise it specifically for the F70 and it looks to have some of the same characteristics of the SCD3, namely low rake and smaller blade area compared to some other props. An advantage of the PowerTech is that as you are experimenting, they'll let you trade for another size prop for a nominal fee. Tim
sailorman	#20  Posted on 11/03/15 - 11:36 AM
Member Posts: 35 Comments: 0 Joined: 01/12/15	I think I'm going to go with the Yahama 70. There is a promotion on for the next two weeks with a $500 rebate on dealer supplied rigging. The extended warranty doesn't apply to engines under 75hp. Tim, which holes did you mount in on your 70?