Jazz up a Yam 15 2 stroke

[flyfshrmn82]

I have an 04 Yam 15 2-stroke and would like to take the next steps to getting more power out of it. What are the next and least expensive ways to go about doing this?

 

[Marv]

Re: Jazz up a Yam 15 2 stroke

It cannot magically make more power, but you can make better use of what it makes with the right prop pitch. And stick a SS prop on it also.

 

[noelm]

Re: Jazz up a Yam 15 2 stroke

buy a 20HP and get a 30% increase in power.

 

[drewmitch44]

Re: Jazz up a Yam 15 2 stroke

Or if you get a wing on your tow trailer, then you can get those flashy valve stem caps, and some ground E-Fex on your trailer. You might feel better about yourself. Yhen you can put some decals on your motor that says that its a 115 instead of a 15. All you need is a extra 1! Then if you run 91 octaine fuel instead of 89 you might just get that extra 100 HP! then all you need to do then is install a fire extinguisher on the door of your honda civic. Then you will have to put some red tape on your busted out brake light. Then remove the duct tape holding the clear plastic sheething on your rear window. Then you wont have to have a second person on the boat to keep squezzing the primer ball so the motor wont quit and just replace the fuel pump gaskets for cripes sakes!!!! Then you will be COOL!!!!

 

[JUSTINTIME]

Re: Jazz up a Yam 15 2 stroke

buy a 25hp

 

[flyfshrmn82]

Re: Jazz up a Yam 15 2 stroke

Or if you get a wing on your tow trailer, then you can get those flashy valve stem caps, and some ground E-Fex on your trailer. You might feel better about yourself. Yhen you can put some decals on your motor that says that its a 115 instead of a 15. All you need is a extra 1! Then if you run 91 octaine fuel instead of 89 you might just get that extra 100 HP! then all you need to do then is install a fire extinguisher on the door of your honda civic. Then you will have to put some red tape on your busted out brake light. Then remove the duct tape holding the clear plastic sheething on your rear window. Then you wont have to have a second person on the boat to keep squezzing the primer ball so the motor wont quit and just replace the fuel pump gaskets for cripes sakes!!!! Then you will be COOL!!!!

Hey dude....don't mistake me for some homie. There's no broke tail lights, no tape, no ground effects, no little fire extinguisher, no Civic, only complete sentences that have grammar, correct spelling, and substance to them.

For the rest of you that replied,

I built a small boat to perfection and have a 15hp on it because weight is key. With a narrow transom on the back, I feel that a 25 would add too much weight. I recently read an article about converting a 9.9hp to a 15hp with only a few parts, and it cost around 100.00. My 15 runs like a champ and pushes the boat along, but I fell that it could do a little more. I run premium fuel through it. I have a SS prop on it with no wear or damage to it. I don't recall what its pitch is though.

I am also exploring the idea of boring it out. That yields a whole set of new questions. How much? What components need to be changed? Where do I look for parts? Just to name a few.

Your help (intelligent responses only please) will be greatly appreciated.

Thanks,
Jes

 

[JUSTINTIME]

Re: Jazz up a Yam 15 2 stroke

well get a tach for that thing and tell us rpm
it is more than 100 to go from 9.9 to 15
u need intake and exhaust and carb
you can reeds, but they do not help much

try raising the motor a little higher

the biggest piston is PISTON (0.25MM O/S)
might look at wiesco also for bigger

 

[flyfshrmn82]

Re: Jazz up a Yam 15 2 stroke

The engine is on an electric jackplate. Once on a plane I jack it up until it feels like it slips or cavitates and go down a little until it feels and sounds like it's running good. I don't have a tac on it, but could install one. What's Wiesco?

Thanks,

 

[JUSTINTIME]

Re: Jazz up a Yam 15 2 stroke

Wiesco pistons

 

[Silvertip]

Re: Jazz up a Yam 15 2 stroke

Here's why people are telling you to get a bigger engine. First, to bore an engine means increasing the cylinder bore which increases the displacement of the engine. You then need to install pistons and rings that are .010, .020, or .030 inch (or equivalent metric) oversize since you now have a bigger hole to fill. Although this technically increases power because of the increased displacement, the increases are so small you will not likely feel the difference. Then there is the issue of porting and polishing. You can modify the porting on a two stroke engine to increase it's power but that requires disassembly of the engine as well and it takes the talent of a good two stroke performance guru to accomplish this. The process produces more power but it is in the upper rpm band and since there is no free lunch, low end performance suffers. Don't you think Yamaha has already optimized the porting on those two engines?? So you see, cubic money becomes involved here as none of the options are cheap. Most engine manufacturers produce a series of engines with two, three, or even four horsepower ratings from the same engine block. (Remember porting??) The factory can do this easily but once an engine is built, its difficult and expensive to do it. So fuel and ignition system timing and induction are often the differences in this otherwise identical engines. Why do they do this if the engines are nearly the same? Some lakes are limited to 10 HP and less. Others are 15 HP and less. That's why. As is the case with the Yamaha 9.9 and 15, it is relatively easy to make a 15 from a 9.9 because a 9.9 is really a detuned 15. But to make a 25 from a 15 is not possible because the blocks are entirely different. In fact in the Yamaha line, the 25 HP stands alone as a 24 cubic inch block. Going bigge the 40 and 50 share a block. And so the story goes. So our advice stands -- buy a bigger motor.

 

[JUSTINTIME]

Re: Jazz up a Yam 15 2 stroke

and going bigger bore, u will need to rejet

 

[flyfshrmn82]

Re: Jazz up a Yam 15 2 stroke

Thanks for all the help. It sounds like boring an engine isn't worth my time. What about boaring out the carbs and changing the jets? What would that give me? Would it give me more than boring the engine? Are there any electronics that I can add or an ECM that can be chipped or changed? Again, I know I can always buy a bigger engine, but to do that will add an extra 50lbs. at least. I am only looking for alternatives, and I know that changing props is one route.

 

[triumphrick]

Re: Jazz up a Yam 15 2 stroke

Or if you get a wing on your tow trailer, then you can get those flashy valve stem caps, and some ground E-Fex on your trailer. You might feel better about yourself. Yhen you can put some decals on your motor that says that its a 115 instead of a 15. All you need is a extra 1! Then if you run 91 octaine fuel instead of 89 you might just get that extra 100 HP! then all you need to do then is install a fire extinguisher on the door of your honda civic. Then you will have to put some red tape on your busted out brake light. Then remove the duct tape holding the clear plastic sheething on your rear window. Then you wont have to have a second person on the boat to keep squezzing the primer ball so the motor wont quit and just replace the fuel pump gaskets for cripes sakes!!!! Then you will be COOL!!!!

WTF??? Are you here to help or you just normally spit out this cr*p?

Just a rough night or are you always pi**ed off and want to feed someone your diatribe. Get a life, dude. I am surprised with your 1000's of posts someone hasn't told you that already.

And that's a sweet looking rig that you have, flyfisherman. Looks snappy with the Yammy. Just what is she pushing? Silvertip makes a good point for not trying anything too radical, however a prop change may be to your best advantage. There are some really good posts by our prop guys and they all are very helpful. Ignore this drewmitch and good luck.

 

[rodbolt]

Re: Jazz up a Yam 15 2 stroke

actually I liked Drewmitch's response
at least I didnt write it.
however getting back to the 15.
not really much can be done with it other than installing a tach and getting it propped correctly for running on the jack.
power trim may help but you would add weight again.
the narrow transom isnt helping at all.
that engine is simply an air pump.
however keeping the air to fuel ratio at about 14.7 to 1 in the cylinders is critical.
thats why you cant just add larger jets or just bore the carb. about the only difference between the 9.9 and 15 2 strokes is the 15 runs a 3 read cage and the 9.9 a two reeed cage.
now you can cut the ports and alter the port timing,finger port the intake side,cut boost ports on the piston,stuff the block modify the reed cage and play with carb venturi diameters.
however its all trial and error and most times the error part allows you to replace a piston.
shaving the head will increase compression some but without extra air and fuel its usually not worth it,in fact extra fuel will be mandatory to combat the extra heat.
that engine can be modified to run on methanol which can boost power out but fuel burn is just over double that of gasoline and requires castor oil or synthetic oils compatible with methanol.
methanol burns at 7 parts air to one part fuel,its octane rating is calculated at 100 and compression ratios can go as high as 13-1 without any issues.
the ign system on that engine is a simple alternator driven setup with movable timer base and a CDI box.
no ECU's nor computer chips.
want more advance simply modify the timer base stop so it can rotate further.
so can more ponies be pulled?
yep.
but nothing cheap,quick nor easy.
but for giggles look up your engines bore and stroke.
to calculate piston displacement the formula is boreXboreXstrokeXnumber of cylinders X .785.
you will then see why boring that motor .50mm wont really affect horsepower thats why we say try to keep the engine well tuned and propped so it can obtain its 4500-5500RPM range.preferably over 5000 RPM so as to lessen the chance of detonation causing piston failure.