1996 Yamaha 9.9MSHU, looking for some input

[linhardt]

Been looking at all the 40 Yamaha conversions and mods and it got me thinking. I acquired a 1996 Yamaha 9.9MSHU that I have on a 1432 Jon. Been thinking I might as well play around with it and see what all I could do to make this into a fine running motor. Was thinking that if I change the reeds to a 15HP reeds, I could get a little more HP out of it. Was discussing this with someone else and they said that I might want to advance the timing 4 degrees after the reed change. Not sure if that is necessary but thought I could look into that as well. Never did timing on an outboards so I will definitely need to research how to do that. Was also thinking about getting a different prop for it as well, not sure what size prop at this point. Might have to do the mods first then get a tinytach and see what my rpms are before I can even get to a point to pick a better prop. Anyone have any experience in modding a Yamaha 9.9 or anyone can give me advice of things I could do on this project? I know that 9.9's are not used much for racing and could not find much on here on modding 9.9's but thought this might be a good place to start to pick a few brains.

[Fastjeff57]

I think the 15 hp has more cubes.

Jeff

[champ20B]

Been looking at all the 40 Yamaha conversions and mods and it got me thinking. I acquired a 1996 Yamaha 9.9MSHU that I have on a 1432 Jon. Been thinking I might as well play around with it and see what all I could do to make this into a fine running motor. Was thinking that if I change the reeds to a 15HP reeds, I could get a little more HP out of it. Was discussing this with someone else and they said that I might want to advance the timing 4 degrees after the reed change. Not sure if that is necessary but thought I could look into that as well. Never did timing on an outboards so I will definitely need to research how to do that. Was also thinking about getting a different prop for it as well, not sure what size prop at this point. Might have to do the mods first then get a tinytach and see what my rpms are before I can even get to a point to pick a better prop. Anyone have any experience in modding a Yamaha 9.9 or anyone can give me advice of things I could do on this project? I know that 9.9's are not used much for racing and could not find much on here on modding 9.9's but thought this might be a good place to start to pick a few brains.

If its a two stroke Yamaha, I know for certain Its a 15 cubic incher same as the 15HP version. I've never worked on a Yamaha, but in most cases with various brands that the 9-15 models shared equal similarities, the difference was often: larger venture carb of same type, and/or higher dome piston, and/or different head, and/or different tuner exhaust pipe (if so equipped). And almost always a higher pitch prop.

The best way to go about this is to get a blow-up diagram of these two models (9.9-15) that has parts identification and compare part numbers. If any numbers are different, change that part over to the right one. That's all that can be done to be sure.

[Fastjeff57]

The same cubes? Good. If it follows Merc's example, the difference is carb throat and tuner. On the 18/ 20/ 25 hp Mercs, the tuner is tiny and restrictive for the 18 hp version, and the carb opening is much smaller.

Jeff

[linhardt]

I have compared diagrams and every part is the same, including jets and carb parts, except for the reeds. The reeds are the only part I see that has different part numbers. The reeds on a 15 seem to have a greater parabolic curve to them than the 9.9. I am sure I could just bend the reeds out more and make a difference, but would probably be better to just buy a set of 15HP reeds. And yes it is a two stroke. But if I change the reeds would the timing need to be changed? Someone mentioned to me that I could advance the timing 4 degrees. If so, how do you do that on a manual pull start? I have seen a video where they did it on a electric start, they just crank the engine via the starter and timed it with a timing light. Do you just hook up the timing light and pull the crank several times? How is it possible to do that with one person? Or is it even necessary? Anyone have an idea of a good prop for it or should I just stick with stock? I have hardly any knowledge of prop performance.



Part Number Part Name Quantity Remarks
63V-13610-00-00 REED VALVE ASSY 1 UR 9.9
63W-13610-00-00 REED VALVE ASSY 1 UR 15

[Fastjeff57]

If that's the case you are in good shape! I would strongly suggest buying the 15 hp reed set up, not taking a chance on ending things. Cheap insurance considering the damage loose parts can do with a 2 stroke.

Any motor can be timed with a light. All you need is a 12 volt battery to run the light, and a solid jumper between the engine block and the battery. Disabling the way the carb is opened allows one to hold her wide open to see where the timing mark is. On older Mercs I simply remove the carb's throttle cam link (one screw).

Jeff

PS: Not sure if your motor has automatic spark advance or not--the later ones do. If so, just rev her up enough to trigger the advance and see where the mark is.

[linhardt]

Per the parts page for my outboard it has 63V-85540-00-00
C.D.I. UNIT ASSEMBLY, which I assume will have the automatic spark advance?

[Fastjeff57]

Easiest way to tell is see if anything under the flywheel moves as you advance the throttle. With automatic spark advance, the stuff under there is fixed in position.

Jeff

[mercguy]

I have compared diagrams and every part is the same, including jets and carb parts, except for the reeds. The reeds are the only part I see that has different part numbers. The reeds on a 15 seem to have a greater parabolic curve to them than the 9.9. I am sure I could just bend the reeds out more and make a difference, but would probably be better to just buy a set of 15HP reeds. And yes it is a two stroke. But if I change the reeds would the timing need to be changed? Someone mentioned to me that I could advance the timing 4 degrees. If so, how do you do that on a manual pull start? I have seen a video where they did it on a electric start, they just crank the engine via the starter and timed it with a timing light. Do you just hook up the timing light and pull the crank several times? How is it possible to do that with one person? Or is it even necessary? Anyone have an idea of a good prop for it or should I just stick with stock? I have hardly any knowledge of prop performance.



Part Number Part Name Quantity Remarks
63V-13610-00-00 REED VALVE ASSY 1 UR 9.9
63W-13610-00-00 REED VALVE ASSY 1 UR 15

yep, only difference between the 9.9 and the 15hp is the reed block......