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9.9 to 15 HP conversion

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SailorDan

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[FONT=Times New Roman, serif]I have a 1985 9.9 HP Evinrude long shaft (10SELCOM) that I use on a sailboat. I have read that the 15 HP Evinrude is really the same engine but with different carbs, a different exhaust tube for at least some model years, and tuned to run at a higher RPM. I am trying to research refitting/re-tuning my current engine for the higher HP.[/FONT] [FONT=Times New Roman, serif]I've looked through the parts lists for the 9.9 v 15 HP engines. It looks like the carbs are almost identical. It looks like all I'd need to do is replace the needle valves, orifice plugs, and exhaust tube, remove the expansion plug, and then tune the engine to run at 6000 RPM instead of 5000.[/FONT] Is that really it? Does anybody have experience with this?
 
The 15 hp carburetor might have a bigger bore !-------I doubt that this modification is going to help much on a sailboat as speed is limited by waterline / displacement.----------What model sailboat is the motor on ?-------------Is the motor equipped with the 10" extension ?
 
The boat is a Catalina 25. I understand it's a displacement hull and that as a result I am best limited to the theoretical hull speed which is just over 6 kts given the 22' 2" LWL.

The engine does have the longshaft extension appropriate to a sailboat, and so the propeller rides in the water where it should. I've had it tuned by a small engine/outboard mechanic. Despite these facts it's rare I get much above 4 kts even though Catalina claims a 9.9 HP engine should be enough to get me to hull speed. Granted sailing days are windy days are wavy days... and that may be part of it. Even on calmer days, though, I don't get anywhere near 6 kts. So I see there being possible benefit in more power if I can get it without adding weight (I wouldn't go up to a 25 HP, for example, as I expect the weight of the larger powerhead might offset any power gains) and especially if I can get it without too much expense.

I've gone through the list of parts for the carburetor and manifold of both engines, and the only difference in parts, unless I missed something, is the needle valves and orifice plugs and the inclusion of the expansion plug in the 9.9 HP engine. Could all the other parts be the same and the carburetor bore still be different?

At some point I may just give this over to the mechanic I've used in the past to see what he thinks, but I figured I'd look in to it some on my own first and see what I could learn.

Thanks for your input and thoughs, I appreciate it.
 
I used to race on a Catalina Capri 25 with a 5 hp Honda.----No problem moving the 3000 lb boat.------------Does your motor have the 10" extension or the 5" extension ????---------Have you verified that the motor now is producing the correct amount of power ????---Did the mechanic run the motor with a proper test propeller ???------Motor may well be running on one cylinder.--------Have you done a compression test ???----------What pitch is the propeller ???-----A fishing boat propeller does not allow the motor to run properly on a sailboat.--------Answers to each question here will get you some more pointers.
 
Thanks again for the input, racerone, and everyone else as well.

The Catalina Capri 25 is a different boat by over 1000 lbs displacement, and so I'm not sure how relevant the comparison is. And my current motor will move my boat. Just not as well as I'd like.

The motor has the 10" extension. I don't have the means to test the power of the motor as it is, and I don't know if the mechanic did. Both cylinders fire. I did check the compression this evening and got 100 on the top cylinder and 105 on the bottom. I haven't found a shop manual on-line for this year yet to double check, but that amount of compression seems low. I didn't think to check the propeller for an actual pitch number when I did the compression check, but it's low pitch and I believe 9 1/4" diameter.

How did y'all figure the 15 HP carb has a bigger bore and that the carb body and jets are different? I've gone through the parts lists for the E10SELCOM I have and the E15ELCOB I assume would be the equivalent 15 HP model, and the only differences I can find in the carburetor & manifold, crankshaft & piston, cylinder & crankcase, and midsection lists of parts are the needle valves, orifice plugs, expansion plug, and exhaust tube.

Thanks again for the help as I try to learn here! :)
 
I've been through the parts lists several times. I'm honestly not seeing/finding it. Just as an example from one area of the engine, looking at

Carburetor & Manifold Parts for 1985 Evinrude 9.9 hp E10SELCOM Outboard Motor

http://www.marineengine.com/parts/j...er=Evinrude&section=Carburetor+&+Manifold

and

Carburetor & Manifold Parts for 1985 Evinrude 15 hp E15ELCOB Outboard Motor

http://www.marineengine.com/parts/j...er=Evinrude&section=Carburetor+&+Manifold

the only differences I find are with #22, #23, and #25. It looks like there was originally a difference between the float chambers (#31), but at some point the chamber for the 15 HP (0319010) was replaced by the chamber originally listed as for the 9.9 HP only (0330881). If one were buying full carburetor assemblies those do admittedly have different part numbers, but getting in to the actual carburetor parts those three are the only one I can find that are different.

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This is very frustrating. I greatly appreciate that you're trying to help me. I don't understand how it is that we are apparently looking at the same thing and yet winding up with very different information. Can you share the links for what you're looking at and a few of the specific item numbers that show up different for you?
 
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As an additional interesting aside I just noticed, it appears the 15 HP models and SEL models shared the same needle valve (0386152) which was eventually replaced by the needle valve for the 9.9 HP (0330884 and later 0432781). So I shouldn't need to change the needle valve. Also, the orifice plug for the SEL models is actually a bit larger than the plug for the 15 HP models (0.056 inch vs 0.054 inch orifice). So I shouldn't need to change that either. It would appear, based on the parts list I've seen, that I'd only need to pull the expansion plug, change the exhaust tube, and have the engine tuned to run at 6000 RPM.

That is, of course, assuming there's nothing else amiss. The suggestion to check the compression was a good one. I can't find any factory specs, and I've seen some people arguing for anything higher than 70 for older outboards being OK and some indicating they wouldn't want less than 120 or so. As I understand it, given that both cylinders on my engine are at nearly the same spot, it seems unlikely there's a compression problem. The question about the propeller is a good one, too. Given we're talking over two tons and a displacement hull, a low pitch propeller seems appropriate. I suppose I could increase the diameter slightly and maybe switch to a four bladder propeller from my current three, both with the thought that it would lead to less slippage. I assume that would come at a cost of lower RPM at WOT, though, and so it might be self-defeating.

I'm learning a lot here. :) :) :) If nothing else I'll have good questions if I take it back to the mechanic later this spring.
 
Is your 9.9 hitting max rpm's?
I think the 15 just breath's better (bigger carby and exhaust and reid's)
The 15hp just revs higher to get the 15hp i think. So if the boat is too heavy for it to rev up higher then the mod is a waste of time and money. Need to get the prop correct on the 9.9 then i'd just try a 2nd hand carby off a 15.
 
Sailor Dan.---------Do you see at the bottom of the list that the 9.9 and 15 have a different carburetor assembly??????--------I own 2 of these SAILMASTER engines and have many more 9.9 / 15 hp models that are for parts and repair.----End of the story.
 
racerone, as above in #11, I do recognize the full carburetor assemblies have different part numbers, and replacing my 9.9 HP assemblies with 15 HP assemblies would do what I'm thinking about doing. But why would I spend several hundred dollars on replacement 15 HP assemblies, which aren't even available from MarineEngine and are thus going to take eBay (thanks to kimcrwbr1 in #7 for the link!) or other scrounging around, when I can just remove the expansion plugs from the 9.9 HP assemblies I have (no cost for parts, only labor!) and part for part have assemblies that are equivalent to 15s -- see #12?

kimcrwbr1, I've read about the regulatory issues that make it beneficial to stay below 10 HP and how the 9.9 HP is just a detuned 15 HP -- clever of OMC to hit two market points with the same set of parts. My current prop is not stamped, or the stamp has worn off, and so I'm not sure of it's measured pitch. Just as an eyeball estimate, at least, it does not look real high.

Anyhow... lots of food for thought. Thank you all for the input. I'll post an update on how it all plays out once it warms up enough to get the boat in the water and I've had a chance to work with the motor some. It did also occur to me that my knot meter could be off and that maybe I've been getting closer to hull speed than I thought. So I'll need to chase that down, too, in addition to checking how much HP my motor is actually making and the high end RPMs.
 
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