Make your 'Rude or Sea Horse 9.9 into a 15!

[jay mendoza]

Converting an Evinrude or Johnson 9.9 hp outboard to a 15hp.

These engines were produced from 1974 to 1992 and after that they underwent significant changes not covered here. From 1974 to 1976 the 9.9 and 15 were identical except for the carb. After that minor changes were a shim under the reed stops, and by 1982 the exhaust tube was changed, but the most significant difference is from 1977 onwards all engines had CDI ignition in place of points. Interestingly, by 1987 both the 15 and 9.9 went back to the 9.9 exhaust tube, so there is little use in bothering with changing it, as OMC eventually determined. The reed shim is a lot of trouble to add for the marginal quickening of throttle response it gives. Of course, if you have the power head off the engine and disassembled, then it would be practical, assuming you have to perform other repairs.

All one has to do is obtain the 15 carburetor of the same year model for the 9.9 and bolt it on to unlock the potential horsepower of the restricted 9.9. It follows that a full service would be wise to do at this time because you will have the pull starter off, and the air box as well, so you might as well pull the flywheel(points model 1974-6) and set the timing while you?re at it. Lube all points as indicated in the manual ; throttle, magneto plate, shifter, and cowl latch. Replace the spark plugs, check the wires. Clean the fuel filter on the pump, and replace any hardened lines, which bring up the following point:

Another thing to note is that the fuel now contains ethanol and most likely the fuel pump diaphragms will need replacement if your engine is over 5 years old, or has not been run in a long time. Although OMC/Bombardier does not list a fuel pump rebuild kit, the kit that is available from Sierra Marine works on 1982 and earlier 9.9-15 fuel pumps, and be advised Sierra does not tell you this either, but the parts are correct. These pumps are a bit tricky to fix, but here is a link on how to do it:
http://www.sschapterpsa.com/ramblings/Rebuilding_fuelpump.htm
Needless to say, I just did mine as well.


Replace the pull rope if frayed(always fun to have it break out on the lake!). Next carefully check that the carb cam follower is synched with the arrow/mark on the cam as they just begin to touch, adjust if required. While you are at it, might as well change out the water pump impeller, or better yet, if you never have done it and your motor is over 10 years old, put in the complete pump kit. Change out the gear oil, and be sure to replace the lower unit drain and fill plug washers with new ones. I might mention you can still get the correct paint, I just re-did my 1975 and the paint matched perfectly, order it from your Bombardier dealer.

The reason I recommend all the extra stuff is because not only are parts getting harder to find, the prices are going up as well. We have no idea how much longer the parts Bombardier has are going to last, or if they plan to produce them once they run out, so get while the getting is good, or be sorry later! Even if you don?t replace now, at least stock up if you plan on keeping the engine. I just bought a spare recoil spring, and the price went up to $20.00 this time!


If you have questions about this, please go to Crowley marine and peruse the on-line parts lists for your year model, comparing the 9.9 to the 15 to find the differences. You will find as I have noted most of the differences are minor and not related to the power head, other than the carb, and exhaust tuning, which as noted reverted to being the same on both models eventually. If you do some research on the engine specs it becomes apparent both models have a much higher full throttle RPM than the rated Horse Power RPM, so they are capable of producing more than their rated power. OMC rated this engine very conservatively as it turns out, and that is why it was popular as a Class A hydro racing engine when fitted with a Quickie lower unit.

 

[JB]

Re: Make your 'Rude or Sea Horse 9.9 into a 15!

Jay, there has been a lot of controversy about this claim. There is a 50% increase claimed by merely changing to a larger venturi carb. There is no verification of identical compression ratios, port size and timing or ignition advance profile. . .three parameters always addressed by racing tuners.

Rather than quibble forever on these and other issues I propose that you call your procedure, "How to hop up your JohnnyRude 9.9 with bolt-on parts" and drop the unprovable claim to 15HP.

The above is a good and complete explanation of how to do that.

 

[ChrisAG]

Re: Make your 'Rude or Sea Horse 9.9 into a 15!

Thanks for your informative post. I have a 1978 Johnson 15 that I bought slightly used in 1979 when I was a kid blasting around the lake with other teens. I raced against various makes of 10-hp class engines, all on 12-14 foot aluminum cartoppers of similar weight. As you would expect, the 15 handily beat them all, which included a Chrysler 9.9, Merc 9.8, and slightly older Evinrude 9.5 and 10.

However, in some cases the difference was only a couple of mph (no GPS back then), and me and my friends figured that if the "tens" were accurately rated, the 15 was only putting out 12 or 13 hp.

I recently saw an old 1981 Johnson brochure online, in which they claim a significant power increase for the 15 starting that year. They boast a 23% increase in top speed with two adults and 75 lbs of gear in a 16' fishing boat. They claim a "finely tuned exhaust and greater engine speed" is responsible. The Evinrude brochure goes a little further, stating improvements in compression ratio and timing. Both divisions claim and increase in fuel efficiency along with the improved power. Also, the full-throtle operating range of the 15 is listed as higher in the spec page than pre-1981 units.

You mention that after 1987 the exhaust reverted back to the 9.9-style, but that might be inaccurate - I read somewhere that the design was slightly different, in effect a 3rd type of exhaust for the 15 (2nd for the 9.9), perhaps keeping the power benefit for the 15 and giving the 9.9 a minor boost for the last few years of the production run (however I have no concrete evidence of this, so you may be correct in stating they went back to the old exhaust).

I figure there must be a measurable gain if they were to make such claims, plus I believe they were motivated to increase the power based on a couple of chages in the industry: increased competition (Yamaha, Honda), and a switch to measuring the horsepower from the crank to the prop (though I'm not sure of the year in which this occured).

All this has me thinking I should track down a 1981+ motor and GPS it against my 1978 model

 

[jay mendoza]

Re: Make your 'Rude or Sea Horse 9.9 into a 15!

JB, there is no controversy here at all, just a little information that needs to be understood:

JB, please go and do the research yourself on this one as you will find that the 9.9 and 15 engine block, manifiold, leaf plate, head, pistons and magneto ignition all have the same part numbers for each year from 1974 to 1987. This is a bit of work, but in so doing you will find that every 3 years there were changes in these part numbers as they kept doing upgrades, but they remain identical between each two models of any year. Once you have done that it should clear things up for you. Of course, if you lived nearby, I would invite you over to come look at all the 9.9 and 15 engine blocks I have laying around, as that would be far easier and more fun.

I have the manuals for both the 9.9 and 15 for 1974,75,and 76. There are no specification differances in compression ratio, bore, stroke, or timing. I have the parts lists for both of these as well and labouriousely researched both of them for different part numbers and only found the carb to be different in the first three years, oh and yes, and the ID tag and cowel decals are different too.

Thus, there is no controversy, the 9.9 and 15 engine block and ignitions are identical for any year as stated. There is no porting,compression, or ignition timing differances.

The first three years (1974 to 1976) of the "Rudes and Johnson 9.9 and 15 were identical except for paint, and the carb, that was it. After that, the 15 had some .0125" shims that spaced the reed stops away from the reeds, and later the exhaust tube was changed, but after that they went back to identical exhaust tubes, as it turns out it just did not make enough differance to warrant two different parts.

As hard as it may be to understand, the 9.9 is actually a 13 hp that is rated at below it's peak horsepower( at a lower rpm than full throttle) so that it would not have to comply with federal restrictions and regulations imposed on engines above 10 hp.

So, a carb is not giving you a 50% increase, as the engine is capable of far more than that. More important to understand is that this engine(the 9.9 version) is severly restricted by a small carb, and unrestricting it allows it to reach it's full potential as a 15hp. Furthermore, look at it's displacement when compared to other 15 hp engines and you will see the 9.9/15 engines are the about the same displacement as most other 15 hp engines, and thus the 9.9 was underated and restricted.

I hope this helps you understand why and how OMC was able to comply with the restrictions placed on 10hp and over engines on federal waterways, they cheated a bit and sold a more powerful motor, but underated it as a 9.9.

All the manufacturers did this too, recall that prior to 1974 there were 10 and 15 hp models, then all of a sudden 9.9 hp models showed up everywhere. They did not make an engine to produce exactly 9.9 hp, they just reved it up on a dyno until they reached 9.9 hp, recorded that RMP and specified that as it's rated output, even if it was capable of more power. So once again, a simple carb change is not giving you 50% more power, that argument is a mute point that carries no water(pun intended). What it does give you however is a bunch more torque and the ability to plane a small fishing boat with a larger load, especially at high altitude lakes where you are down on power anyway.

Remember how Mercury used to market their engines? The KE-4 Rocket was sold as a 7.5 hp when it actually put out around 10hp. This was to make them appear more powerfull and a better value for their size as a sales promo.

 

[pecheux]

Re: Make your 'Rude or Sea Horse 9.9 into a 15!

I owned both a 1981 Johnson 9.9 (still own) and a 1980 Johnson 15 ... and found them to be 2 different beast. The 9.9 revs at approx 5500 - 6000 rpm the 15 reved at approx 7000 - 7500 rpm. Asked my OB mecanic to upgrade my 9.9 to a 15 and the list of things to do far exceeded what has been proposed on this board and was not recommended for $$$$ reasons. I wished it would have been that easy ... apparently not.

 

[jay mendoza]

Re: Make your 'Rude or Sea Horse 9.9 into a 15!

Get the parts lists and do the research for yourself, it's not at all what your mechanic told you, the only differances in that year model are the leaf plate shims, the carb, and the exhaust tube. The leaf plate stopper shims and exhaust tube are not needed to make more power, as they alone will do nothing without the bigger carb. The real impediment today is the cost, and availlability of the 15 hp carb, which is no longer availlable. Look at the prices these fetch on eBay, there has to be a reason they are in such great demand and get those ridiculouse prices...because they work! By comparison, 9.9 carbs are availlable and inexpensive on eBay. I'm glad now that I paid $78.00 for my 15 carb in 1982, even though it seemed like an awfull lot of money back then.

So he is right it's not practical today, due to availabilty and price, but had you done it years ago, it would have been cheap and easy.

I have a simpler suggestion for you however that will proove beyond a shadow of a doubt that the carb makes a huge difference: Since you have both engines, just swap carbs and give them a try. If you lived nearby, I'de do it for you as it's so simple and easy to do that it takes less than an hour.

In my experience with these engines, the 1977 through 1987 models were plagued with power pack problems and I have always avoided them due to that. By contrast, my breaker point magneto 1975 model has never fouled a plug or failed to start due to an ignition problem in the 27 seasons I've operated it. There is something to say for that, which is the old adage about keeping it simple....

 

[JB]

Re: Make your 'Rude or Sea Horse 9.9 into a 15!

JB, there is no controversy here at all, just a little information that needs to be understood:

Hahahahaha!! That is the biggest load of misinformation I have heard lately, Jay.

I am not stupid, Jay. I have engineering, business and education degrees and used to make part of a living writing technical manuals and teaching engineers how to teach.

It matters not whether you or someone else is correct. What matters to a moderator is whether or not people fight over it

Since you persist in arguing about it this thread is closed. Bring it up again and risk suspension.