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Old 29 August 2009, 12:02   #1
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upgrade yam 15 is it possible

was speaking to a guy on the slipway this wekend and he said i could convert my yamaha 15hp 2 stroke by changing the carb is this this right ?
as my 380 is plated for a 25 i would like to do this if its possible
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Old 29 August 2009, 12:22   #2
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Bear in mind that possible and practical are not always the same thing.

e.g. My 20HP Yam 2str CAN be upgraded relatively easily to the 25HP which was based on the same design. To do this I would need to replace the carbs and the exhaust manifold. To make use of the extra power I would need a new prop as well - that lot would add up to around 500 assuming I fitted it myself. Probably easier to sell and buy a replacement.

For someone to be able to confirm if there is a "simple" route to upgrade - they will need to know the model and year.
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Old 29 August 2009, 12:34   #3
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Quote:
Originally Posted by Dino89 View Post
was speaking to a guy on the slipway this wekend and he said i could convert my yamaha 15hp 2 stroke by changing the carb is this this right ?
as my 380 is plated for a 25 i would like to do this if its possible
A Yam 15 HP has about 250 cc a 25 has about 450 cc, it's a complete different & bigger crankcase and engine. If possible everybody would be doing that for a very low cost.

Happy Sibbing
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Old 29 August 2009, 16:15   #4
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Yopu can uprate a 9hp to a 15hp but the 20 or 25 are different engines. Tohatsu get 18hp out of the same block in their range though - 9.9 - 15 and 18hp so you may get more with a different carb etc.
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Old 30 August 2009, 13:42   #5
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a lot depends on the cubic cap,,,as the other posts say with some block models eg , 8 hp..9.8 hp same block and cu cap . then 9.9....15 hp same block and cu cap and so on usually if your engine is of the lower rating it can be a case of just changing the main carb jet and perhaps the timing a little ,i have done it with some of the older yammys ,,,,i converted a 9.5 to a 12 many years ago then comes the old myth issue of the smaller rating engine perhaps lasting longer than the bigger one ,
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Old 31 August 2009, 12:33   #6
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thanks for the info will stick with it as a 15hp ,nowi want add remotes and steering but thats a whole new idea
thanks again
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Old 31 August 2009, 17:16   #7
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thanks for the info will stick with it as a 15hp ,nowi want add remotes and steering but thats a whole new idea
thanks again
Don't know if I would bother. The whole beauty of a 15hp 2 stroke is it's light weight. ideal for lugging about. If you are going to literally tie it to your boat you may be better off selling it as they make silly money and getting a 25hp with remotes etc already fitted.
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