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Thread: 9.9 to 15hp

  1. #1
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    Default 9.9 to 15hp

    I've got a 2000 Basstracker with a Mercury 9.9 2 stroke. The boat is way underpowered, but my parents live on a 10hp restricted lake, and this seemed to be the best bet nearly 20 years ago when we got it. It has always ran flawlessly, but a couple tanks of ethanol gas last year has it in need of a carb. I have heard that the only difference in the 9.9 and the 15 was the carb. Does anyone know if that is the truth? If so I may put a 15 carb on to see if it will help at all. Right now the boat is close to getting on plane when it's just me, but any added person and it just plows. Anything other than the carb needed, and any recommended sites to order from? Thanks in advance!

  2. #2
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    I can't say with any certainly on your Merc but I know with Yamaha they do what you're talking about. But it may not be quite as simple as you think.

    For instance, the only difference between the 3 cylinder 40hp 2 stroke and the 50hp big brother is the carb jet and the exhaust tuner. There's your extra 10hp. They do the same thing in the 25/30, the 60/70 and the old 75/85/90. I know Merc does it on the 40/50/60 59ci block as well as well as the 20/25 2 cyl. I'm confident Merc does it on others as well.

    The best way to compare is go to Mercury's site and find the part breakdown for both motors. Go to the carb and compare the part numbers. The body of the carb is likely the same, but just the main jet is different. Most carbs have 2 jets, one that feeds fuel into the motor when it's at idle, and the other when it's basically anywhere past idle speed.

    Then for reassurance, check out the exhaust tuner that comes out of the mid section to see if those parts are the same. If not, then you'll have more than just carb jets to change to get those extra few hp out of her.

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    Last edited by willyworm; 04-15-2018 at 06:39 PM.
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  3. #3
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    You really have to look it up by make and model year. My nissan 15 is the same as a nissan 9.9 except for 30 dollar throttle plate.


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  4. #4
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    Thanks for the replies. I've been on the Mercury parts page for an hour, and I cannot find a single part that is different between the two. Starting to go cross eyed. I will call tomorrow to see if there is an actual human being that I can speak to, however I do not have high expectations that Mercury would willingly tell me how to convert a 9.9 to a 15hp.

  5. #5
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    If you can't find out, let me know. I know the Mercury Commander and I will find out.

  6. #6
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    Ersepton- buy the 15hp carb and you are good to go

    Willyworm- the difference is more than tuner and jet on the motors you specified. There’s a big difference in Yamaha 40 and 50 carbs. Plain as day the throats of the carbs are much bigger on the 50 than the 40. If you put a 50 main jet in the 40 carb you will run rich all day and make less hp than a properly jetted 40carb. Same as 60-70 carbs. Yamaha 25 and 30 too.

  7. #7
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    I looked on the Mercury parts page, and they appear to have the same carb, same jets etc. I cannot see a difference on the parts list, across the board.

  8. #8
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