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Johnson/Evinrude 9.9 to 15 hp conversion

Anyone have info for this, aside from the carburetor change? This is for a 1990 model. It was 11 years ago, but when I tried to do the "common" conversion via carb swap only, it didn't work. Results were: raw fuel out the exhaust, no significant power increase. After contemplating this for several years, I have come to the conclusions: The exhaust tube for the 15hp is different than the 10hp, the exhaust ports in the 15(exhaust housing casting) may be different than the 10, the timing advance cam may be different. There is absolutely no info regarding this in the service manual or parts list except: I saw a different exhaust tube in a photo of something unrelated in the service manual. Johnson went to the trouble of being sure the necessary info was not available in their documents. I have not found a dealer who was helpful in any way. Does anyone have a genuine 1990 15hp for sale so I can get the necessary parts, or any info for this to satisfy my curiosity?

Edits: 50/42/00

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Topic - Johnson/Evinrude 9.9 to 15 hp conversion - DB 12:21:07 03/04/02 (2)

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