Johnson/Evinrude 9.9 to 15 conversion

[jay mendoza]

OK, I have had enough of all the miss-information spread by people answering questions about converting a 9.9 to a 15. The answer is plain and simple, and it is yes you can and it very easy to do.

From 1974-81 the only differances are the carburetors. After that the 15 had a different exhaust tube, and some small .0125 spacers under the reed stops to allow the reeds to open a bit more.

Now, that said, I have a 1975 9.9 and put a 15 carb on it. The power increase was so significant that it promptly broke the upper motor mounts and I had to replace them! Next I tried a 15 exhaust megaphone and the reed shims, which did not seem to make any noticable differance, the biggest single change is the carb, pure and simple.

All the guys who have posted here saying you can't just change the carb and that there is much more to it than that to get the 15 hp are dead wrong and obviousely have never done it themselves, ignore their comments. I'm here to tell all of you that if you can get a 15 carb, it will make a really nice power boost to the 9.9hp Johnsons and Evinrudes(1974-87) Beware that you kind of need to get the same year model carb, as your year however, as a plastic carb does not adapt well to an ealier engine( all metal carb) without some modifications.

Another thing is that some have said the 15 won't idle and troll as well, but that is exactly what I use my engine for when the wind is not strong enough to drift troll, and I have never had a problem...and I like to troll very slowly.
I went back to using the 9.9 hp(1975) exhaust tube as I found it was quieter, and removed the reed shims. I then re-bent the reed stops to allow the reeds to allow the reeds to uncover more of the opening in the leaf plate when open, and that resulted in crisper throttle response and acceleration, but no measuable increase in top speed.

The one thing that helped with super low idling was to set the points timing dead on using a strobe type timing light, this revealed they were off quite a bit as compared to checking with a battery powered light, buzz box, or just gaping to .020" with a feeler gauge. Once both points were set dead on the money as verified when running with the strobe timing light, the engine ran much smoother and idled down to lower speeds than was previousely possible.

 

[tashasdaddy]

Re: Johnson/Evinrude 9.9 to 15 conversion

my question is >>> did it really make it a 15 hp, has it been tested or is this just your opinion.

and yes, you did much more than just change the carbs, which is the rumor, about converting 9.9 to a 15 hp.

 

[DGartzos]

Re: Johnson/Evinrude 9.9 to 15 conversion

I am all with your point here.

Practically did the same things to my 40HP and got lots more power out of the wider throat carbs alone. I got rid of those reed valve leaf stoppers altogether, pistons will suck what they need, reeds are there not to allow backward flow of mixture so there is nothing much to gain of converting the stoppers. However, they may be protecting the leafs of damage that may occur, if they open right up to the crankcase. Did not happen on my motor so far.

I would also like to see a more willing approach to conversions !!!

 

[Bob_VT]

Re: Johnson/Evinrude 9.9 to 15 conversion

Hmmm interesting concept you have there. Make one post in one thread over a year ago and make another ID and start a thread with the same information.

WHY? This has not been a recent topic of discussion and I would classify this as a troll. How tired can you be with 2 individual posts over a year apart.

 

[Lion hunter]

Re: Johnson/Evinrude 9.9 to 15 conversion

I'm not going to doubt that you did it and this is not ment as a flame. But I am curious about the motor mounts. They should have been the same as a 15 so any increase in HP shouldn't have broke them unless they were already ready to break. Also you stated that your setting were off quite a bit. Could it be that your 9.9 was running like a 7 and your tuneup helped as well? There has also been a great number of posts that have tried what you did and did not suceed for whatever reason. Also when most ask about increasing hp they are looking for a silver bullet. I've got a 9.9, and if I had a 15 carb laying around you can bet I would have to try it. But if I had to incur any costs I might as well sell the 9.9 and buy a 15. Anyhow if it really worked for you, good job. Was the increase in speed by gps?

 

[JB]

Re: Johnson/Evinrude 9.9 to 15 conversion

So you put your hopped up 9.9 on a dynamometer and got 15HP? Oh, you just know that it is now 15HP?? That is really interesting.

And you did all this instead of what old timers on here said you would have to do. Ummm. . .What did you do differently??

That is what I thought.

 

[iwombat]

Re: Johnson/Evinrude 9.9 to 15 conversion

Nobody here has ever denied that you can get a performance increase by changing carbs. However, that's never what anyone asks. The question is always "can I make a 15hp"? You still haven't answered that question.

 

[Lion hunter]

Re: Johnson/Evinrude 9.9 to 15 conversion

One other question I would have is how exactly do you set point gap with a timing light? I am no super mechanic by any means but I can't for the life of me figure out how you have access to the points when the engine is running.

 

[tx1961whaler]

Re: Johnson/Evinrude 9.9 to 15 conversion

A decent experiment would be to have both a running 9.9 and a running 15 HP motor, GPS the 9.9, then switch the carbs, then GPS the 9.9 with the 15 HP carb. Then do the same with the 15 HP on the same boat (and same prop). Granted, the motors will not be in identical condition (not quite apples-to-apples comparison) but you'd have 4 speed results: 9.9/9.9 carb, 9.9/15 carb, 15/9.9 carb, 15/15 carb. If it were only a carb difference, then you'd expect to see the same top end speed difference between the two motors with different carbs, and roughly the same top end out of either motor with the different carbs:
[GPS(9.9/15c) - GPS(9.9/9.9c)] ~ [GPS(15/15c) - GPS(15/9.9c)]
GPS(9.9/15c) ~ GPS(15/15c)
GPS(9.9/9.9c) ~ GPS(15/9.9c)

Too bad I have neither a 9.9 nor a 15......and a dyno would certainly be more scientific...

 

[Whoopbass]

Re: Johnson/Evinrude 9.9 to 15 conversion

I bought a 1981 15 hp Evinrude for cheap and while I was cleaning the carb I noticed it was actually a 9.9 carb.
I had a 15hp carb on hand and so I went to the river to check the performance difference.
My boat is a little heavy for the 9.9 but it got up to a little over 17 mph slowly. I swapped carbs and the 15 hp carb got the boat up to a little over 20 mph quickly (gps speeds). Not a whole lot of difference in speed but plenty of low end torque and pick up speed with the 15 hp carb.
I've gps'd my boat with a 25hp Evinrude @ 25mph and a 30 hp suzuki @ 27mph.
Even with double the hp I only got a 7 mph increase in speed but a whole lot more hole shot and I was able to get up to speed quickly.

I think you guys are splitting hairs here. Whether a carb swap makes any outboard a true 15hp or not really doesn't come into play that much since double the HP only relates to a 33% increase in speed. If someone did measure the HP difference between the 9.9/15 carbs on whatever combination of motors the percentage would be so small that it really wouldn't be noticeable in real world conditions.

 

[Lion hunter]

Re: Johnson/Evinrude 9.9 to 15 conversion

It's tough to extrapolate any information when comparing the 15 and the 30. You did double your hp but maybe doubled the weight as well which would have negated some of the hp gain. With a 15 and a 9.9 all the variables except hp are equal, so the increase should be easily measurable. I wouldn't be interested so much in dyno measured hp as an increase in gps'd speed. Also on your test between carbs you detuned the 15 with a 9.9 carb. There should be no problem other than loss of some hp. The issue is going from a 9.9 up. Most reports I have read state the engines gets to much fuel with some reporting that it doesn't run right until wot.

In any event if the original poster is truly a troll then he has accomplished his goal of creating a pointless discussion.

 

[Whoopbass]

Re: Johnson/Evinrude 9.9 to 15 conversion

I have a 9.9 and a 15 hp carb that I could test but what would be the point since several people on here would try and disprove the results. They might be right but they are being to technical. I have read a couple other posts where people have done the carb upgrade and have been happy with the results.
Bottom line is if you do the carb upgrade your outboard will still run fine and you will get a big increase in torque. Top end gain is only a few mph.
I think the upgrade is worth it because an underpowered rig struggling to get up to speed sucks.

 

[tashasdaddy]

Re: Johnson/Evinrude 9.9 to 15 conversion

Whoopbass, not disagreeing, you can get some improvement, but the thing is you will not get 15hp.

i still have not seen any 'REAL' results, on on a dynamometer

 

[Lion hunter]

Re: Johnson/Evinrude 9.9 to 15 conversion

Whoopbass, I to am not disagreeing with you. And even though It would be nice to have dyno results I would be happy with gps results. We never get that. Anecdotal evidence such as ,It must have more hp, the motor mounts broke, doesn't prove anything at all. As for what the point is, As far as I'm concerned the point is if you have the parts to do it and can gain even 1-2 mph then go for it. But it hard for others to give advice on such a conversion. Like was said before, people ask can I turn a 9.9 into a 15? Probably not. Can you get more speed with a 15 carb, maybe. It would be nice to get the results from such a test. Along with any increases in speed it would be nice to learn how it runs at all throttle positions. With all that said if you can put a 15 carb on a 9.9 and it makes you happy then go for it, you have nothing to prove to any of us. But unless there is good information it is wrong to convince someone to spend money on a carb to do a swap that may not yield the results they expect.

 

[hopscotch840]

Re: Johnson/Evinrude 9.9 to 15 conversion

I am all with your point here.

Practically did the same things to my 40HP and got lots more power out of the wider throat carbs alone. I got rid of those reed valve leaf stoppers altogether, pistons will suck what they need, reeds are there not to allow backward flow of mixture so there is nothing much to gain of converting the stoppers. However, they may be protecting the leafs of damage that may occur, if they open right up to the crankcase. Did not happen on my motor so far.

I would also like to see a more willing approach to conversions !!!

You used the carbs off of which motor on your 40 hp? What year 40 hp?

 

[DGartzos]

Re: Johnson/Evinrude 9.9 to 15 conversion

My motor is a '94 40HP E40EERE and used carbs of a '89 50hp Johnson with part # 0432987. They have a wider throat as original and different orifice plugs.

 

[jay mendoza]

Re: Johnson/Evinrude 9.9 to 15 conversion

For those who just don't get it, like Tashdaddy(who is a wonderfull source of miss-information, listen to him if you want to really get confused) just give it up. If Lion Hunter and Tashdaddy are correct, then that means Johson/Evinrude/OMC is also lying about how much power the 15 makes. You see they argue that my changing the carb cannot make it a 15, but if they are correct then the 1974-82 15 are not 15 hp either, as mine is identical to those engines in every way. I used the parts lists to confirm this. Who do we believe? OMC, or two hodads, who like to spam the board and call people trolls when they are prooven wrong.

All I initially did was bolt on a 15hp carb, and I'll tell you, the boat really improved, the BIG differance was being able to plane it with three people as opposed to two people, now thats a significant power increase. Get real, like I'm going to get a dyno or take out a GPS.....the boat hauls *** now, thats proof enough.

How do you set the timing with a strobe light? Simple, you check it with the light, note how far it is off, remove the flywheel, tweek the points, put the flywheel on again and check with the strobe, repeat unitl it's exactly on. Besides, you missed the point(pun intended): use the strobe light mainly to spot the timing junping around, which a static DC light won't show. Once the engine is statically timed, it is very close and only a slight tweek is required to get it dead on identical while running by the above method. You guys must really think I'm stupid eh? NOT!

For all you guys doubting the power increase, or the amount of power increase, or if it really is a 15hp, you are out in left field, once again, sad to say. Go ask OMC/Bombardier, not me, I just updated my engine.

The first thing is this: The 9.9 is rated 9.9 hp at about 5000 rpm, but it will easily rev to 5500 rpm or more where it is making more than 9.9 hp, in actuality it makes about 12 hp at around 5600 rpm. The top rpm depends on the prop you are using and the load on the boat.

The secong thing is that the 15 hp makes about 18 hp if you put the correct prop on it as it will rev up to 6800 rpm or more.

The third thing is who cares about peak brake horsepower when its peak torque that pulls you out of the hole and puts you on plane? The 15 carb alone is a very significant increase in power for the early 1974-82 series 9.9 engines. The different exhaust tube on the 15 that was used from 1982 onwards does not significantly affect peak HP, but it does help torque a little, again it was not enough for Johnson/Evinrude to change their specs on these engines. (note that they remained the same regardless of the years)The difference is the carb, it is the key to unlocking the hidden power in the 9.9.

Anyone here who says different has never done the conversion and is just speculating; I myself have done it and am very happy with the significant power increase and performance. Notice the two main detractors here have not done the conversion, so there you go!

For further creedance and to disscredit all the doubting Thomas' we have seen posting above, I was guided on how to do the conversion by a Master OMC technician, John Gil. He went to OMC school back when the 1974-76 Johnson 9.9 and 15 compacts first came out and specialized in them as the Marina where he works has a fleet of over 50 rental fishing boats using 9.9 engines(Johnson) John would go back for refresher/update courses about every 2-3 years until the Bombardier buyout in 2001. John used to be at Big Bear Marina with Larry Cook, but for the last decade he has been the top mechanic at Holloways and is one of the most experienced and respected OMC mechanics in California.

One last point: I spent over $90.00 back in 1984 to get that 15 hp carb, and at the time it was relatively expensive. Had it not resulted in a significant power increase I would have not only been dissapointed, but very angry with John , neither of which happened. Instead I was richly rewarded for my efforts and consulting an OMC expert and 9.9 /15 specialist on how to make my engine a 15. John incidentally is the one who told me the 9.9 and 15 are both capable of higher horsepower, it's just that they are rated at a lower RPM than the full throttle RPM, where they both make more power than the stated rating.

Sorry to dissagree, but some people here insist on perpetuating miss-information, and it is really not helpfull, as the correct answer is YES, you can make a 9.9 into a 15 with just the carb, it's just that simple. Futhermore the other differances(1982 and onwards) are not significant or required to get 95% of the improvement the carb alone gives you. The people who insist on arguing this are focusing on trivial insignificant points that in reality don't have much to do with anything. You have disscredited yourselves by calling me names, and inadvertently insinuating that OMC must have been lying as well, and aditionally admitt to never having done the conversion. So much for your credibility. There are a couple guys here (see above) who have done the conversion and agree its for real, as it should be. Who are we to beleive? Are we to beleive OMC, and the guys who have done the conversion, or two other guys who have never done it and like to call people names when their "authority" and fragile ego is challenged? What a joke, they call me a troll just because I've got a life and haven't posted a million times here. I'm still laughing at that one, it's that stupid.

I'll never forget once I had converted the engine to a 15hp, we went and raced 440 Jet Skis off of Doheny Beach outside of the Dana Point breakwater and could out run them in a straight line, which was never possible before, and the 12 foot Western would start to chine walk, it was thrilling to say the least! Made me want to get a SS lower unit and build a Clark Craft Hydro, I may still do that someday.

 

[Lion hunter]

Re: Johnson/Evinrude 9.9 to 15 conversion

I was going to argue until I found out you know John Gil..........WTF is that?

You obviously have a chip on your shoulder for some reason. You come on here and after 2 posts and some anecdotal information about hp increases, expect everyone to disregard everyone else and drink your kool-aid. I don't think thats going to happen. Tash would not have gotten to the point of moderator disseminating bad information. Has he been wrong, probably. Who hasn't (except you and John Gil of course). Really dude, give it up. You are not trying to provide information, you are trying to flame other members.

 

[DGartzos]

Re: Johnson/Evinrude 9.9 to 15 conversion

I am putting here my story, it may be of help.

I've got a '94 40HP evinrude and have been running it standard for over a decade. I never thought of a conversion or was willing to pay money for one, until i got for free two carbs of a 50HP scraped motor and that's how it all begun. Simply bolted the carbs on and there it was. My boat, a 13' RIB 900lbs total weight would fly out of water and response to throttle became absolutely immediate. With standard carbs it would take 7 to 8 seconds to planning and with wider throat carbs within 3 seconds it is out of water and within 6 seconds is flat out 34.5 mph GPS. Now that is significant increase on power and it is of the carbs alone.

Since i got involved with conversion i have tried to find out more and looked on the intake and exhaust possible differences. Having been through part numbers of 40,45,48,50 and 55HP motors i concluded that there could not be many other differences, namely:

i) nothing much on reed valves (except reed leaf stoppers on the 40HP, which i got rid of altogether, but with not a noticeable difference),

ii) nothing much on exhaust housings (one part number for the 40,48 and 50HP and another for the 45 and 55HP),

iii) nothing much on cylinder heads (one part number for the 40,48 and 50HP and another for the 45 and 55HP)

and that leaves the engine blocks between the 40 and 50HP with different part numbers. A not cross referenced hint i got elsewhere on the net, says that the 50HP has the exhaust port 0.048" higher on the cylinder sleeve than the 40HP giving to it that extra power top end. However, the 45 and 55HP use the same engine block and their 10HP difference is due to the carbs olny.

Why not open a forum category on conversion ?

 

[JB]

Re: Johnson/Evinrude 9.9 to 15 conversion

Anything useful has been said. This thread has turned into an argument and has come to an end.