Convert Mercury 9.9 to 15

[billyb33]

Gentleman - wondering if anyone on here has successfully converted a mercury 9.9 to a 15 hp. I have a 2004 9.9 two stroke Mercury. I've read conflicting stories on the good ol' internet. Some say a simple carb swap and new exhaust parts is all that is needed others advise against it and say it will wear out a 9.9 by converting to a 15hp. Any advice or help is greatly appreciated! Thanks

 

[flyingscott]

Edit sorry I read that as 2009 not 2004 yes it can be converted to 15 hp. Do what ondavr says about looking at the parts. The 9.9 was built on the 15 hp block starting around the early 90s. As long as that is not a tohatsu built motor.

 

[MH Hawker]

it can be done to a select few motors. 1995 to 2000 that i am aware of, i did it on my 1996 motor. how ever the first thing to look at is the part numbers for both motors

 

[ondarvr]

At about that time they increased the displacement of the 9.9 to be the same as the 15, I can?t remember the exact year though. Either way you need to pull up the parts diagram and match up each part number to see what parts are different.

 

[Sea Rider]

Remove cowl and post both lateral side views of the powerhead to check if it's a Merc or Tohatsu OB, If it's a rebadged Tohatsu it's a throttle cam & cab swap + advance timing depending on which 9.9 model you have. Both are 250 CC powerheads being the 9.9 a restricted OB.

Happy Boating

 

[billyb33]

No Title

Thanks guys. I'll print out the parts diagrams and compare the two. Below are pics with the cowling off of both sides. I hope it's a genuine Mercury.

Also, I ran the motor yesterday in my driveway in a bucket and just notice the liquid coming out of the prop in the below pic. Doesn't look or smell like lower unit fluid. Any idea what it is? Is this normal? I'm a little worried as this a new to me motor and was supposedly in excellent condition.

 

[Sea Rider]

It?s not a rebadged Tohatsu. It's a Merc, some says this version has Yam powerheads which don't know about. The black substance if gummy coming out prop is 2 strokes/fuel leftovers going down from exhaust. Normal on 2 strokes engines.

Happy Boating

 

[billyb33]

Thank you all. Really appreciate you guys

 

[billyb33]

Motor ran great today but I noticed the water coming out of the tell tale was rather hot at times and just warm at others. At one point I couldn't keep my hand on it for more than ten seconds. Is this a normal characteristic of this motor?

At idle it was a weak stream but water flow got steadier under throttle.

 

[flyingscott]

That is normal. I would double check the thermostat and make sure it has a 120 deg in there.

 

[Sea Rider]

At idle engine pees water at a much less temp than when at throttle passing idle. That's because thermo opens more or less depending on throttle operation & temp. If worried about working temp, install a new thermo.

Happy Boating