# crazy upgrade idea



## czuniga (Apr 3, 2012)

Hello. 

Crazy idea so I'm trying to upgrade my 1980 9.9 Johnson to a 15 HP. These is an idea until a bigger hand tiller comes along.. so I called my local marine place to ask for parts and a quote on labor.. guys tells me wecan get a ccarb that shouldn't be hard to find but the exhaust or megaphone might be tough to find..so he suggested we can bore a couple of holes on the existing exhaut as long its above the water line. Has anyone ever heard this before


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## Johny25 (Apr 3, 2012)

I don't think you need the exhaust horn on a 1980 to make it a 15hp. All you need is the carburetor and the shim that was added in 1979 to the 15's. It goes behind the leaf valves & under the stop plate. It is part number #325038 and it is .0125" thick. 

I did this mod on my 87' and actually bought (and still have) the shims not knowing if I needed them but they were already in my 87'. If I were you I would do this mod myself unless you don't mind paying the extra money for a marina to do the work. To get to the exhaust you will have to remove the powerhead. And to be honest when doing mine I didn't see enough difference in the exhausts to actually make a difference. But I put the round 15hp one on anyway since I was already in there and already had bought it.

Oh an this is not a crazy idea by the way. I did it and had a very noticeable improvement. I went from not being able to get my boat on plane to planing at a decent clip. You will notice it to if done right : )


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## Johny25 (Apr 3, 2012)

Look on ebay for the exhaust horn, I paid $40 bucks for mine off there. And I can tell you if is the correct one if you give me the number off ebay if you aren't sure if it is the correct one. Because in 85-86 they went to prop rated HP so maybe if you really want 15hp (at the prop) you will need this exhaust probably. But I believe in 1980 the 9.9 and 15hp used the same exhaust horn. But I doubt they were really making 10-15 hp back then, hence the changes to the same motor over the years to get a few more ponies : )


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## czuniga (Apr 3, 2012)

Where does this shim goes? I will look into it. The crazy ideaq was to drill a hole on the existing ehaust. Without replacing it with a new one. He suggested lets try the carb and if needed lets drill the existing exhaust


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## Johny25 (Apr 3, 2012)

Ok well if you remove the power head (which is required to get to the exhaust horn) then you may as well put the correct one on instead of drilling it out. The shim's go between the leaf stops and the leaf valves. What it does is allows the leaf valves to open a little further for better air flow.

Here is a link that will help you (about 1/4 of the way down the page)
https://www.sschapterpsa.com/ramblings/Johnson%209.9_15.htm


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## czuniga (Apr 3, 2012)

I have been researching and the exhaust is the same for the year of the outboard I have. I just need to change the carb to a 15 HP. And the shims if I wnna go the extra mile. Do I need to remove the powehead to get to these shims. I think I could do it myself. Does anyone have a pic of how to install them. Or a 15 HP carb up for sale. I've been on eBay for a while and they are. Not easy to find


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## Pappy (Apr 4, 2012)

Do not drill out the exhaust...will just make the engine louder and drive people crazy.....does nothing for horsepower. 
Yes, find the megaphone and you will notice a difference. The change came about around 1981 or 1982 (look it up if you care to) and along with the carb it makes a stout 15hp engine. While there change out the water tube grommets at the top of the water tube as well. These have a nasty habit of collapsing around the water tube and restricting cooling water to the powerhead. They collapse due to overheats and, if around salt water, corrosion.


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## czuniga (Apr 4, 2012)

As per my research the megaphone is the same. It did does not change for my engine since its a 1980 so ill be Hunting for a 15 HP carb I thnk its the same carb from 1980 TO 1986 I Believe. Also its recommended toinstall shims. Just have no idea where these are suppose to go. Do I need yo remove the pwerhead for this.


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## Pappy (Apr 4, 2012)

Yes, you are correct in your research, however if you want more horsepower than the shims and carb will give you then add the megaphone. It is a direct replacement for the inner exhaust pipe on your older version engine.
The shims are spacers that are placed between the reeds and the reed stops to allow the reeds to open a little farther. You will have to remove the intake and reed boxes and disassemble the reeds from the boxes to accomplish this. Much more seat of the pants horsepower will be gained by going with the megaphone. Make sure you utilize loctite on re-assembly if you do install the shims. If you don't necessarily trust the information coming your way it may do you well to look at the profiles of those who offer information. Some of us have "been there ,done that".


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## czuniga (Apr 4, 2012)

Thanks great info


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## Johny25 (Apr 4, 2012)

FYI your motor is going to become a lot louder when you put the 15hp exhaust horn on. Not to mention your engine RPM will increase by 500-750 rpm.


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## Johny25 (Apr 4, 2012)

Go to the link I gave you at sschaptera, it shows exactly where the shims go.


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## czuniga (Apr 5, 2012)

would i need to exchange the horn. I ive read a couple of threads it only give you about .5 of hp increase. Im wondering if for my 1980 the carb is the only difference. ive been looking for some online. i guess ill start with that and give it a try.


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## Pappy (Apr 5, 2012)

Okay....lets go over this one more time. Prior to around 1982 there was no exhaust megaphone, only the lowly exhaust pipe. The changes were in the carb and reeds. OMC Engineering took advantage of the tuning in that engine and developed a megaphone or (tuner) to enhance the midrange and top end horsepower of the engine platform. That particular engine was an early one to make it to propshaft horsepower with these new modifications and it was on the plus side of allowable. To make your engine into a later model 15hp you will need to add the tuner or megaphone. The horsepower difference is seat of the pants in some boats in acceleration in particular. Much greater than the .5 horsepower you may have read (was that person in OMC Engineering and have access to the dyno sheets? I doubt it ). To date I have updated at least 6 engines that I can think of with the carb and tuner and all customers have had a nice grin factor. There is no audible difference either with or without the tuner that I have heard and have run tons of these engines over the past 35 plus years. There will be no difference in idle quality with the addition of the tuner and carb. The job is an easy one to do. From here on it is up to you.....


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## czuniga (Apr 5, 2012)

Found the round exhaust on a salvage place online. Couldn't find anything on eBay. Guy is suppose to try to find me a carb to go with it. Ill make sureto compare the carbs before I install them. I'm also checking out the shims online. I think ill be aable to tackle it once I get the parts.


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## czuniga (Apr 6, 2012)

One more question is there a gasket or something I need to buy to install the exhaust


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## Johny25 (Apr 6, 2012)

Yes you will need to replace the power head to exhaust housing gasket.


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## Johny25 (Apr 6, 2012)

I will humbly disagree with you pappy about there being no audible difference between the 9.9 and 15hp due to the exhaust horn. The 15hp round horn is a few inches shorter and does not seal to the lower unit like the 9.9 does. This causes less of the exhaust to be pushed through the prop which increases the exhaust sound that comes out of the port in the back of the midsection. The 15hp exhaust creates less back pressure this way also, giving more HP. But the noise increased noticeably on my 87' when I did this mod, and I expected it to anyway given the different exhaust. Also your engine is going to run 500-750 RPM higher which also increases noise.

Well worth it though for an extra 5 ponies : )


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## Pappy (Apr 6, 2012)

The only increase in noise level I can think of would be coming as a result of the increase in RPM and therefore a pitch change and possible increase in noise level. At higher RPM almost all noise heard is coming from the intake and reed noise so that should increase with additioonal RPM. The idle reliefs in the exhaust housing passed the same Db level no matter the inner exhaust exhaust due to the fact that the exhaust gas has to pass through a wall of water. What can make them louder is to drop the static water level thereby dropping the wall of water. If you started yours on a hose for the first time after modifications or in a shallower tank you may have heard a difference (and that stuck into your memory) but the wall of water designed into it did not care which inner exhaust was in it. Next time you have one completely apart look at the way the water and exhaust flows and you will see what I am talking about. That tuner cannot have an effect on it unless you change the static water level at the same time. I have one apart at the shop and will see if I can get a photo of it for you if you care to take this any farther. Don't know if the photo will show well enough but I will look tomorrow for you.


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## Johny25 (Apr 6, 2012)

I would like to continue this but I do not want to gum up this gentlemens thread with our debate. I will PM you : )


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## czuniga (Apr 6, 2012)

Is these where the shims go


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## Johny25 (Apr 6, 2012)

Yes, right under the leaf stops and on top of the valves. So in between them.


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## czuniga (Apr 6, 2012)

So I remove those flaps and install them underneath


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## czuniga (Apr 6, 2012)

Great pic. Hopefully this thread can help someone else in the future. I think I get it. I removed these two screws and install the shims right under them. Question I would just be raising the leafs a little bit. How would this improve performance


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## Johny25 (Apr 6, 2012)

Your raising the leaf stops and not the leaf valves. With the stop leafs being higher up it allows the valves to open up further. Essentially they will bend open farther. Make sure you get them back on correctly. Do one side at a time so you can always reference to the other side and so you put the same leaf stop back in the same spot. The leaf valve is also referenced to as "the reeds" and it is just a very thin piece of metal that opens and closes to allow air and fuel to the crankcase.

Do not put them under the leaf valves! Just so we are clear put them on top of the leaf valves (thin metal flapper) and underneath the leaf stops (the thicker metal stops that do not bend or flap). I hope this clears up your question : )


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## Pappy (Apr 6, 2012)

*Johny25* - I will gladly defer to you on the exhaust. I looked at one this afternoon (mid -80s) and the dam does not go all the way to the top as I thought it did so there may very well be a difference in noise level although I have never noticed it. Good job!
On the reed screws.... make sure loctite is used on re-assembly. This was already mentioned in an earlier post. Also make sure the water tube grommet or grommets are replaced during the changeover. Cheap and needed.


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## czuniga (Apr 11, 2012)

Anyone happen to know if I would need to replace any gaskets for the leaf plate. If been trying to oder the head to exhaust housing. And the water tube gourmets. But iboats can't seem yo find what I'm talking about.my shimssand carb should be on the way. Missing the megaphone. Can't seem to find one. Just want to get all the small parts in. Anyone happen to have part numbers. 

Thanks


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## Johny25 (Apr 11, 2012)

Yes replace both gaskets, one on each side of the leaf (reed) plate. Also replace the gasket between the carb and intake manifold. What parts are you needing numbers for? Please be specific


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## czuniga (Apr 11, 2012)

The part numbers for these gaskets and the gasket for the power head to exhaust. Thanks


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## Johny25 (Apr 11, 2012)

Exhaust to powerhead gasket #0325721
Intake manifold gasket #0325260
Reed plate to crankase gasket #0318924

And get a carb rebuild kit for your new carburetor #0398453

All these parts can be looked up on this site https://www.marineengine.com/parts/johnson-evinrude-parts.php?year=1980&hp=15&model=J15RCSD&manufacturer=Johnson&section=Carburetor+%26amp%3B+Manifold

boats.net usually is the best for prices that I know of but if you don't live near Florida then it takes forever for the parts to get to you. I only buy from boats.net when I am not in a hurry for parts. I didn't have time ti look the water tube grommet up but you can do that I am sure :lol:

DO NOT BUY SIERRA GASKETS OR PARTS! GET OEM ALWAYS!


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## czuniga (Apr 12, 2012)

Is this the exhaust I need to purchase. Just want to know. For some reason Ihought it was completely round


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## Johny25 (Apr 12, 2012)

No that is not the exhaust you want. The one you want is round on one end. That link I gave you earlier in this thread shows exactly what you need. The exhaust on the right is the one your looking for.


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## czuniga (Apr 13, 2012)

Thanks I appreciate it.


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## czuniga (Apr 13, 2012)

Question,, 
once i get the shorter exhaust i replace the water tube from my old exhaust right. Does the water tube need to connect from the top all the way to the bottom?

thanks


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## Johny25 (Apr 13, 2012)

You can use the water tube off the one you remove. It should fit just fine. Yes it needs to connect to your impeller housing in the lower unit and also at the top in the exhaust grommet or else you will have no water flow, with no water flow engine will overheat a seize. First thing to check after the mod is that water is flowing properly : )


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## czuniga (Apr 16, 2012)

Is this it. The short tube looks like plastic.


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## Johny25 (Apr 16, 2012)

Thats not the best pic in the world but yes it looks like the correct one. And I cant tell if that is plastic or not but it should be copper tubing. You can always make one from copper tubing from the hardware store. When I bought mine it had no to and I just used the one from my 9.9 square exhaust.


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## czuniga (Apr 16, 2012)

Guy tells me its off a 15 and thats round. I think ill just go for it. Thanks. Ill post better pics once I get it.


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## Johny25 (Apr 16, 2012)

Well that exhaust in the pic is definitely round and it looks like the correct exhaust. The lighting in the pic is terrible though. But if it is a fair price get it : )


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## czuniga (Apr 16, 2012)

40 bucks and my carb just came in. Found it on clist gentleman was selling a lower unit and agreed to sell me carb if I would send a prepaid package. For 35 bucks u can't beat it


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## czuniga (Apr 16, 2012)

40 bucks and my carb just came in. Found it on clist gentleman was selling a lower unit and agreed to sell me carb if I would send a prepaid package. For 35 bucks u can't beat it


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## Johny25 (Apr 16, 2012)

Order a carb kit so you can rebuild the carb, order an exhaust to power head gasket, and order a new rubber grommet for the copper water tube to go into and you are in business.


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## czuniga (Apr 16, 2012)

Gaskets ;kit and shims should be on their way. I should be getting everything by sometime this week.


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## czuniga (Apr 24, 2012)

Hi

So all my parts are in. Where do I start. The carb is not a prob. However the intake is my question do I need to drop my lower unit. And then get to the powerhead. Also the shims have a straight side and curved side does the curved side should face theflaps. Also where exactly iis the leaf plate.


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## Johny25 (Apr 26, 2012)

Ok this has nothing to do with the intake. It is the exhaust that you need to do. You need to get the powerhead off to get to it so you will need to disconnect everything that needs to be disconnected in order to get the powerhead off. Once all is ready then remove the 6 powerhead bolts from underneath and lift the powerhead straight up. It will most likely be stuck to the midsection so you will have to tap it sideways or carefully pry a screwdriver between midsection and powerhead to break the gasket loose. once the gasket is broken loose lift the powerhead straight up until you can clear the midsection with the exhaust tube. The lower unit does not have to be removed.

This is a pic of my johnson 30hp powerhead off to give you an idea what I mean by removing the powerhead. I can't find my pics of when I did my 9.9 so this is the best I got.


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## czuniga (May 3, 2012)

Hello.
So I finally got around to do my upgrade. Had a little trouble alinging my water tube. But I eventually got it going. Definately sounds louder. I have not taken her out to the water so I cant really tell how faster she is. I hope she does well with my prop. Which is 9 pitch .


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## fender66 (May 3, 2012)

czuniga said:


> Hello.
> So I finally got around to do my upgrade. Had a little trouble alinging my water tube. But I eventually got it going. Definately sounds louder. I have not taken her out to the water so I cant really tell how faster she is. I hope she does well with my prop. Which is 9 pitch .



You mean to tell us that you didn't take pictures of this mod? Shame on you! [-X 


:LOL2: :LOL2:


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## Johny25 (May 3, 2012)

Yes pics would have been nice so to help others in the future. Glad to hear you finished it. Yes it will be louder as we mentioned before. But that means extra horsepower :mrgreen: I guarantee you are going to notice the power difference in the last 1/4 turn of the throttle.

The 9 pitch may or may not work depending on the load you have in your boat. Now that you have a 15hp your recommended operating RPM range is now 5500-7000 instead of 5000-6000 with the 9.9 but I would stay around the 6250-6500 mark if I were you. My guess is you could go to a 10 pitch and get a little more speed out of your boat. Get a tach so you can make sure to have the correct prop for your NEW engine


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## czuniga (May 4, 2012)

Thanks for all the help and great ideas. Ill try a test run with my nine pitch and then ill try my 10 again. Ill let u guys know how it turns out. Yeah I was so carried away I forgot to take pics. But like you mentioned very easy to do.


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## Fudoshin (May 14, 2012)

I have a Mercury 1996 7.5 hp motor, is there a way to make this go faster? I am new to the boating world, but I am mechanically inclined just do not know to much about boat motors...yet :mrgreen:


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## Johny25 (May 14, 2012)

I thought I remember seeing something about a merc 7.5 mod but I myself do not know enough about mercs to tell you what or if it can be done.....


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