1998 Johnson 9.9hp 2-stroke conversion to 15hp

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JanKsterS

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I've done a bunch of reading on these forums about the pros and cons of doing this - that is not what I am asking about. I just want to know how I can figure out what the differences are between the motors so I can purchase and install the parts to safely upgrade it to the 15hp.

I live on a lake that has a strict 10hp limit.

So once again, how can I figure out what parts need replaced, and where can I buy these parts?

Thank you.
 
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boobie

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Re: 1998 Johnson 9.9hp 2-stroke conversion to 15hp

Go to shop.evinrude.com and look up the mtrs and compare part #'s.
 
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the machinist

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Re: 1998 Johnson 9.9hp 2-stroke conversion to 15hp

On that motor all you need is a 15hp carburetor.
 
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JanKsterS

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Re: 1998 Johnson 9.9hp 2-stroke conversion to 15hp

machinist,

Are you positive? I haven't had a chance to do a component comparison yet but I am very excited to hear that. Hopefully there are carbs available on ebay.

JanKsterS
 
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the machinist

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Re: 1998 Johnson 9.9hp 2-stroke conversion to 15hp

The situation is that the motor was designed as a 15 hp and detuned for the 9.9 hp. The only difference between the 9.9 and 15 hp motors of this 1993 to 2001 series, is the carburetor (which has a larger throat) and the decal on the side of the cowling.

For more info, go to my LeeRoys Rambings website

If you try to get one on eBay, be very careful that it is indeed a 15hp (larger throat) and the right choke version (manual or remote electric). Some of those wontabee outboard parts sellers have no clue what fits what. And the 15hp carbs are priced at a premium because of the exact reason you are wanting to change over.

After 2001 they went to a completely different & not interchangable with the early carbs.

You will not find new 15 hp carburetors even listed as a separate saleable part anymore. And they never sold just the body.
 
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bonzoscott

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Re: 1998 Johnson 9.9hp 2-stroke conversion to 15hp

AND beware of those Ebay items that read 15Hp!
 
Faztbullet

Faztbullet

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Re: 1998 Johnson 9.9hp 2-stroke conversion to 15hp

The intake manifold is different as is the reed plate,,,add these and a carb and its a 15hp. Usually all you need to do is open throat on manifold.
 
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JanKsterS

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Re: 1998 Johnson 9.9hp 2-stroke conversion to 15hp

Faztbullet,

I am looking on shop.evinrude.com at my motor (J10RELECC) and the 15hp (J15RELECR - is this the one I should be comparing against?) and I am not seeing where their intake manifold differs. Can you tell me how you know this is the case? Machinist has a pretty in depth website that backs up what he is saying. I want to be doing the right thing here to keep my motor in good shape and get the extra power...

Also, machinist, my dad has a 15hp Johnson Carb from sometime between 1975 and 1985. Sorry for my uninformed question, but am I able to use any carb from a 15hp or do I need to use the corresponding year of my motor (1998)?
 
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the machinist

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Re: 1998 Johnson 9.9hp 2-stroke conversion to 15hp

I think that the manifolds may have had a larger entrance hole to match the carb throat on the EARLIER models, but later on & after the new series came out in 93, they pretty much used all 15hp parts for the 9.9hp but the carb. As far as I know the only difference at the reed plate was for the later (1979 & newer 15hp), they added a shim under the reed stops to allow the reed to open farther.

You will need to stay within the model range when changing carbs. You can not go back any farther than 1993 because at that time they changed the choke lever system. And in 2002 they went to a totally different carb, but I have not totally evaluated those yet. Anything earlier than 93 will not hook up to your choke lever.

Then sometimes, especially on the pre 93s, the throttle arm roller was made different sizes. These had to match the throttle cam otherwise your "Link & Sync" timing would not be able to be set.
 
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Jim311

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Re: 1998 Johnson 9.9hp 2-stroke conversion to 15hp

Yeah I don't think there was any difference other than the carb in those years. It's hard to find a correct carb, though, from what I've seen.
 
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JanKsterS

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Re: 1998 Johnson 9.9hp 2-stroke conversion to 15hp

Thanks for everyone's input. Machinist really helped me out and even found a carb that will work for me on ebay. It's purchased, now I just have to open the box and install it. I'd like this thread to be left open so I can come back and post my results.

JanKsterS
 
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JanKsterS

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Re: 1998 Johnson 9.9hp 2-stroke conversion to 15hp

Successfully installed the carb last weekend. Used a photo tach after installation to measure RPMs, they were high now on the prop I was using prior to the installation. Changed prop out from 9.25"by8p to a 9.25"by10p, RPM's were optimized.

Results:

The motor, stock, was pushing my decked out, 14 ft grumman at 14mph tops.

After the carb swap and prop change, I was topping out at 19mph.

I couldn't be happier with the results - the extra 5mph was well worth the $150 I spent on the carb. I can get around the lake A LOT quicker now to my fishing spots, it is A LOT more fun to go for a boat ride, and I can pull a knee boarder now - will try skiing soon.

JanKsterS
 
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JanKsterS

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Re: 1998 Johnson 9.9hp 2-stroke conversion to 15hp

Oh yea, and thanks to machinist for all his help!
 
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