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Old 17-10-2010, 00:58   #31
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I think you will need the new bigger carb to allow more air and fuel, so the motor will rev higher and thus allowing more power
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Old 17-10-2010, 01:13   #32
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Originally Posted by boris View Post
I think you will need the new bigger carb to allow more air and fuel, so the motor will rev higher and thus allowing more power
Being a 4-stroke, probably a new camshaft as well..
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Old 18-10-2010, 08:48   #33
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I'm looking at doing the same thing to my 9.9 but was told it woudn't give any more power. Also it would seem to me that a new prop would be in order. Where did you find the Merc parts diagram?
Here's the link to the ones for my model:

Mercury Outboard Parts 2002 1010312Zd
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Old 31-05-2011, 12:51   #34
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Re: Converting 9.9 Merc Two-Stroke to 15hp

I finally did it. I changed the carburetor and adaptor plate(w/ exhaust tube). Got a 20% increase in top end speed. Now I just have to change the decals. If you do it too, make sure you buy a new adapter plate gasket and powerhead gasket because mine were fused to the metal. I recommend Mercuryperformance.com for their price and customer service.
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Old 01-06-2011, 07:57   #35
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Re: Converting 9.9 Merc Two-Stroke to 15hp

Don't change the decals. In the street racing world, you would have a "sleeper".
Make some bucks in the marina racing
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Old 01-06-2011, 08:09   #36
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Re: Converting 9.9 Merc Two-Stroke to 15hp

Do your research The ob builders often use the same block for a family of motors but often the porting in the block is different Compare the part number for the block as well. When I sold suzuki motors Their 3 cyl 25 hp motor was excatly the same as the 30hp but with a throttle stop on the carbs to limit throttle opening
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Old 25-08-2020, 20:41   #37
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Re: Converting 9.9 Merc Two-Stroke to 15hp

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Originally Posted by elmcken View Post
I finally did it. I changed the carburetor and adaptor plate(w/ exhaust tube). Got a 20% increase in top end speed. Now I just have to change the decals. If you do it too, make sure you buy a new adapter plate gasket and powerhead gasket because mine were fused to the metal. I recommend Mercuryperformance.com for their price and customer service.
I have been searching for the 15hp carb for years now with no luck. I am going to try to change the jet and bore out the throat of the carb. I have send the carb to get xrayed to see where the internal channels are so I know where to machine. My 10hp carb throat diameter is little over 20mm (0.8"). If anyone here can tell me what the 15hp carb throat diameter is, I will appriciate.
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Old 29-08-2020, 21:26   #38
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Re: Converting 9.9 Merc Two-Stroke to 15hp

It seems 10hp has room to go to 25.3mm throat diameter max.
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Old 01-12-2020, 11:11   #39
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Re: Converting 9.9 Merc Two-Stroke to 15hp

Does anybody know if I can do the same with my 8HP 2001 Mercury 2 Stroke?
Was told it is same as 9.9 Except for carb.
So question is can I put a 15 HP Carb on it and get same results?
Any input would be great
Thanks
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Old 28-04-2021, 07:08   #40
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Re: Converting 9.9 Merc Two-Stroke to 15hp

Here is a picture of a 9.9 carb and a 15hp carb mine had the round choke knob, the 9.9 is the bottom one, si its more than just jets

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Old 19-06-2021, 05:40   #41
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Re: Converting 9.9 Merc Two-Stroke to 15hp

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Originally Posted by Roy M View Post
I took an outboard repair class last summer from a local community college. My assigned motor was a Mercury 9.9. The difference is the jet in the carburetor. All the other goodies are the same engine. The reason? California freshwater areas are apparently limited to ten HP.
What year model was this? I'm working on a 93 Mercury 15 hp and have a donor motor that's a 92 9.9 and the Carb on the donor is newly rebuilt. Wondering if the carbs are interchangeable with the only change being the jet?

Thanks!
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Old 19-06-2021, 06:15   #42
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Re: Converting 9.9 Merc Two-Stroke to 15hp

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Originally Posted by Dukestek View Post
What year model was this? I'm working on a 93 Mercury 15 hp and have a donor motor that's a 92 9.9 and the Carb on the donor is newly rebuilt. Wondering if the carbs are interchangeable with the only change being the jet?

Thanks!

You'd need to look at the blow apart parts diagram to see if in fact it is only the jets that are different. Some of those motors also had different exhaust systems to handle the increased hp differences.

Could always try it to see if you had any noticeable difference in performance w/the larger jets.
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Old 19-06-2021, 06:42   #43
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Re: Converting 9.9 Merc Two-Stroke to 15hp

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You'd need to look at the blow apart parts diagram to see if in fact it is only the jets that are different. Some of those motors also had different exhaust systems to handle the increased hp differences.

Could always try it to see if you had any noticeable difference in performance w/the larger jets.
Thanks,

The Blocks are the same along with pistons, crank and block reed mount so I'm pretty sure they are the same. Carb's have same bore on air intake side and the slight neck down in the middle is same.
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