1985 9.9SK upgrade to 15hp

[909909909909]

Is it possible to upgrade a 1985 9.9 to a 15 by bending the Reed valves to 6mm

Are there any other differences between the two outboards other than the reed valve spacing?

[909909909909]

Found someone already did this on a 2006 engine but was wondering if it would work on a 85::

I thought I'd start a new thread just to do with this work. I had read a lot of threads online and today I decided to convert my newly acquired 9.9 to a 15hp.

This is a 2006 engine, but as I understand it, the engine design didn't really change for about 20 years from mid nineties til a couple of years ago.

There are two aspects to doing this work:
1. Adjusting the reed valves
2. Removing the throttle limiter.

First off was adjusting the reed valves.

The reed valves sit on a plate between the carb and the block, so to get at it you need to remove the carb. These 2 10mm bolts go through the plastic airbox (?) and the carb.


There were then various linkages between the throttle and choke mechanism. Most uncipped, but I found that I needed to undo this screw, which attaches the choke mechanism onto the side of the plastic airbox.



I also had to loosen this screw to slide this linkage out. I marked its position with a marker pen.


Once the linkage was loosened, I could rotate the carb to the side, without removing the fuel line. This revealed the reed valve plate

[909909909909]

There are 3 10mm bolts holding on the reed valve plate.

This is the reed valve. Notice one side I have opened out and one is in the stock condition:


I had read of people opening the reed valve out with pliers, but I was worried of twisting it, or damaging the rest of the assembly, so I removed the plate and rigged up a bending fixture in my vice, using a bit of brass I found.



I needed something flat to bend out the clearance, and settled on a bolster chisel.


My feeler gauges don't go up to 6mm, so I measured various things in my toolbox til I found something that was right. (I've since heard of using a 6mm drill bit, which would have been easier!)

[909909909909]

The second stage was the "rev limiter", this was a little tab, which stopped the throttle fully rotating. I was thinking about bending the tab, but didnt want to strain the mechanism. I also thought about remving it totally, but was worried that when I remved the bolt it would spring apart. Not sure what to do, I decided to losen the bolt slightly to see if I could rotate the tab. After a couple of turns, the tab just fell off - it turns out that its slotted. So this bit was very easy:




And that was that. I ran out of time, so I haven't fired her back up. I also received a tachometer in the post today, so I'll have that installed for when I fire the engine back up.

[909909909909]

Bump

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[ausnoelm]

Not too sure why your are "bumping" you are telling us how it's done (though I am not sure it's all correct) so, why bump the thread, test the motor and get back to us, then read both parts manuals for both models to see what else is different.

[99yam40]

and find a dyno to measure the HP difference to be sure

[909909909909]

Is it possible to upgrade a 1985 9.9 to a 15 by bending the Reed valves to 6mm

Are there any other differences between the two outboards other than the reed valve spacing?

Found someone already did this on a 2006 engine but was wondering if it would work on a 85

This is someone else's work on a different engine and mine is a different year and am asking if it will work on my year

[ausnoelm]

The very first step is looking at the parts manuals for BOTH models, comparing every part to see what different, then go from there. Lots of motors share a common basic block for multiple HP, similarly lots of people say "it's just the jets" or "it's just the carb" but in reality there can be multiple different parts to add 50% more HP rather than just bending some reed stops. Not saying it can't be done, but the principal is, you get more air/fuel in, it needs to get out, meaning it can be an exhaust difference too, or a cylinder head, or a piston or the ports in the actual block that can't be changed.