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Old 06 October 2009, 20:17   #1
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Johnson 9.9 4 stroke

Does anyone no if I can modify this to uprate it? I seem to remember someone on here saying that the 9.9`s are all de-tuned 20hp or something like that. If it can be up-rated, how do I do it and what is the most I could get out of it?
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Old 06 October 2009, 20:44   #2
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Does anyone no if I can modify this to uprate it? I seem to remember someone on here saying that the 9.9`s are all de-tuned 20hp or something like that. If it can be up-rated, how do I do it and what is the most I could get out of it?
Thanks
Are you thinking of using it as an aux? If you are, I wouldn't bother uprating it.

Not sure if the 4 strokes can be uprated anyway-AFAIK it's a few of the old 2 stroke 9.9 lumps that were a 15hp with a restriction.
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Old 07 October 2009, 05:40   #3
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johnson 9.9 4 stroke

No it`s not for an aux I have a tiny rib 2.9m and I was thinking about putting the engine, console steering etc onto a 3.5m rib so would need more power that`s why I was wondering if it could be up-graded to 15/20hp.
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Old 07 October 2009, 07:55   #4
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johnson 9.9 4 stroke

I think I remember that Hugh Jardon may have done a thread about up-rating the hp of a 9.9 but i think it was a fair time ago and I can`t be totally sure.
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Old 07 October 2009, 14:51   #5
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I think I remember that Hugh Jardon may have done a thread about up-rating the hp of a 9.9 but i think it was a fair time ago and I can`t be totally sure.
He did-but it was specifically for a Yamaha 9.9 2 stroke. It's here:-

http://rib.net/forum/showthread.php?...ghlight=yamaha
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Old 07 October 2009, 18:24   #6
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It depends on the specific model.

For example the 2006 Suzuki DF9.9 4 stroke can be upgraded to a DF15 by replacing the carburettor. The 2009 DF9.9 is actually a beefed up DF8, so cannot be upgraded.

If there is a Johnson 15HP that has the same vital statistics as the 9.9 (ie bore, stroke, compression ratio, gearing, weight, etc) it might be possible.

You need to compare the parts lists. If the only difference is for example the carb, it may be possible if you can do it cheaply enough. If it is the camshaft, ignition system or a number of other things it is likely not worth the hassle.

First step may be to see how much you can trade your 9.9 in for against a 15.

Cheers

Chris
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