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Old 14-02-2016, 11:54   #1
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Tohatsu 9.8 to 15 hp conversion

I have hear a rumor that a Tohatsu 9.8 (4 cycle) can be run as a 15 hp with a change of Carbs? Any truth to this? If so I expect the prop will need to be changed too?
Any Wisdom?
I have a 2006 Tohatsu 9.8 (4 cycle) that is still running well but sometimes with 4 persons in the dingy a little more pwr would be nice.
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Old 14-02-2016, 12:17   #2
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Re: Tohatsu 9.8 to 15 hp conversion

Not true. the 15hp motor displaces 351cc and weighs 114lbs. The 9.8 displaces 209cc and weighs 81lbs.

Completely different motor.
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Old 14-02-2016, 13:04   #3
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Re: Tohatsu 9.8 to 15 hp conversion

Compare engine weights. If approximately the same, it's possible though the mod might be more complex than simply removing restriction plates or other easy changes. In the 2 stroke Tohatsu models, it's the 9.9 that can be modified to the 15; the 9.8 is the bored out 8 which is in itself an opened up 6.

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Old 14-02-2016, 13:55   #4
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Re: Tohatsu 9.8 to 15 hp conversion

Anyone know I'd the Evinrude yachtwin 8 two stroke can be modified to the 15? I thought I saw it somewhere when I did work on it but unsure if it was mine.

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Old 15-02-2016, 08:03   #5
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Re: Tohatsu 9.8 to 15 hp conversion

Look up the displacement of the 8 and 15. I'm betting not. Some 9.9 two strokes could be easily converted, in some cases because they had been de-powered to 9.9 due to a lot of inland waters prohibiting motors 10 hp and over.
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Old 15-02-2016, 08:09   #6
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Re: Tohatsu 9.8 to 15 hp conversion

Quote:
Originally Posted by Brewgyver View Post
Look up the displacement of the 8 and 15. I'm betting not. Some 9.9 two strokes could be easily converted, in some cases because they had been de-powered to 9.9 due to a lot of inland waters prohibiting motors 10 hp and over.
That was the case for my old Honda 100. The 15 was an identical motor.

I'm not sure why anyone would risk damaging the motor/voiding the warrantee for such a small gain.
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Old 15-02-2016, 08:32   #7
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Re: Tohatsu 9.8 to 15 hp conversion

If I may piggyback on this thread, I have a yamaha 15hp that, from what I've been told, can be converted to a 20hp. Not sure I'll bother, but is anyone familiar with that process as far as degree of difficulty and cost?
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Old 15-02-2016, 17:04   #8
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Re: Tohatsu 9.8 to 15 hp conversion

The 2 strokes had air restrictions to de power them. Nissan tohatsu did not do that . The power head was different between the 9.8 and the 18 horse. The 9.8 was a 2 stoke.
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