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1981 99 Mariner OB 25 shaft

C

ctalmage

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"I have a 1981 9.9hp Mariner o

"I have a 1981 9.9hp Mariner outboard 25". Is it possible to convert this motor to a 15hp? I've heard possibly changing the carburator or removing a restrictor plate may up this to 15hp. I need to get more oompf out of it to push a 28' sailboat. Any thoughts or suggestions?
Thanks,
Cal
[email protected]"
 
"Cal, if it's an 81 then i

"Cal, if it's an 81 then it will be a 9.8 not a 9.9 (which didn't come into production until 86).

In any event, pre-94 Merc 9.8/9.9's could NOT be converted to 15 horse, the powerhead did not have the necessary displacement. The pre-94 9.somethings were the biggest motor in the model, sharing a head with the 7.5 (in the case of the 9.8's) and the 6/8 horse in the case of the 9.9's...."
 
"Thanks Tony - didn't come

"Thanks Tony - didn't come to mind when I answered him, but sounds like you are right.

If that's the case then I have to change my answer to "I don't know"...

The motor is a Yamaha and I don't know what they were sharing their powerheads with back in the early 80's - although they were building all the powerheads for the Mercs at the same time..."
 
"Cal,
To get a little more go

"Cal,
To get a little more go out of that motor you should be able to use a carb off a 15hp Yamaha of the early 80's. Im pretty sure they shared the same powerhead."
 
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