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MercuryMariner 99 to 15hp

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realjoe2000

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"I have a 1995 mariner 9.9, ca

"I have a 1995 mariner 9.9, can I swap the powerhead with a used one of a 15hp merc or mariner. How are they different? Are the mercs compatible with mariner? Im just learning how they work. Im sure the carb may be different. Any big differences if I should find a good 15hp powerhead? Is there lots of different changes I would have to make? Thanks"
 
"Joe, provided that the Marine

"Joe, provided that the Mariner is a Merc built Mariner and not a Yamaha built model, the swap is direct.

The 15 Merc is also a direct swap.

A 1995 9.9 is exactly the same powerhead as a 95-on 15 horse anyhow, only the carb and exhaust plate/tube is different.

The 94 and earlier 15 horse powerhead (back until 1988 - again Merc built only) will also bolt right on no problem.

I own a pair of 9.9's and a 15 horse. I swap them out occassionally on my rig - 14' deep v, full console (total weight 850 pounds loaded).

The difference (although not scientifically tested) is the 15 horse gives me 3 mph more at the top end under ideal conditions - and burns about 40% more fuel.

If you can make the swap by obtaining parts for next to nothing, sure go for it, but if you have to open your wallet I would advise against it - you may be disappointed. If you really want more power, sell your 9.9 and get a 20 or a 25..."
 
"Thank you for taking the time

"Thank you for taking the time to explain about the Merc swap. Ive learned a ton allready and its much apreciated. My idea for the swap to 15hp was for more power and speed for hunting with a 14' modified V Jon boat. I hunt large lakes and sometimes I need to get off fast. With decoys, guns, shells, dog, etc the 9.9 is a might limited so now I see it wont get me much more to spend the money on an upgrade. A 20hp might be the answer, but there alot heavier. Thanks again for the information."
 
"Yes - like I said my tests ar

"Yes - like I said my tests are not scientific by any means - but I do own both 9.9's and a 15 and have tested them with numerous set-ups such as different props, hydrofoils, played with the trim etc and they really are pretty much the same motor as far as "on boat" performance goes.

And while the 18/20/25 weighs in at about 20 pounds more than the 6/8/9.9/15's, they really do have an extra "umph" that you notice..."
 
"I have a 2003 15 HP, 4 stroke

"I have a 2003 15 HP, 4 stroke Merc.

The engine is like new with only 20 hours on it.

At idle or low speed it runs poorly, fine at high speed. I burn only high octane gas, sometimes adding a little gas line antifreeze to address the ethanol challenges.

Is there a simple low speed adjustment on the carb and if so, where would it be locasted?

Thank you."
 
"Rupert, if you click my name

"Rupert, if you click my name and drop me an email, I can send you something on the carb.

However, carbs do not just "go out of adjustment". What you describe, despite your best efforts, sounds like a clog/varnish issue at the low speed jet.

"Only" 20 hours on a 5 year old 4-stroke is a major part of the problem. You have to run these little motors. Far more die from not being used than being over-used.

If you have no other option, even putting them in a bucket or on a flusher and running them for an hour or so each week will add years to their lifespan..."
 
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