# 15 hp Yami Issues.



## cutrunner

Chances are your plug wire, coil, cdi, and stater will Never go bad.. Yamahas just good at electronics, unlike merc. Its either you missed something in the carb, it needs new plugs, or you messed with an adjustment. ( dont take that the wrong way as i dont know your mechanical abilitys)


----------



## AfterHours2

Thx for the quick reply. Im going to try out the plugs today. I don't think it has anything to do with the carb because it is acting the same way before/after the carb clean. I could be wrong though. Thx for the info.


----------



## cutrunner

Make sure to use the ngk plug it calls for. Dont cross refrence to a champion or anything else


----------



## AfterHours2

NGK all the way!


----------



## AfterHours2

Well after a quick plug change and some fresh gas the motor is still doing the same thing. Its odd because it only happens when you put a load on the motor. Ive pretty much done all the basic fixes to the motor and now Im scratching my head on this one. Could it possibly be something in the lower unit. When you hammer the throttle down it is very sluggish and eventually picks up speed later on for a little while then slugs back down. Any other opinions please....


----------



## Brett

Have you tried running it after dark with the cover off?
One of the easiest ways I know to find arcing circuits
that aren't visible to the eye during daylight hours.
Anything that interferes with your ignition will slow you down.


----------



## bsdbum

I have been helping some (not much) trying to get this motor running right.  I can add that we did a full carb break down but did not adjust any needle's or HS / LS screws.  I have been thinking it seems like it could be a carb adjustment issue from the low speed to the high speed circuit.  When we rev the motor it seems to run strong and turns high RPMS up to the rev limiter.  The problem shows up when the motor is under load.  Could it be a hi speed screw that needs to be opened up?  

If someone could give me a good starting point for what the screws should be at that would be helpful.  Also we did a compression test and 130/130 each hole.  Plugs look a little white we are running 50-1 fuel ratio. 




Thanks for the help!!


----------



## floridanative1028

I'm not %100 positive but I think that engine is supposed to run on a 100:1 mix.


----------



## cutrunner

Whatever you do , DO NOT adjust any of the screws. I hate to say it but you must have missed something in the carb, its not hard to do in those little motors, especially japanese. Heres how you find out what it is, and please try it before tearing into unnessecary things. Running the motor on land will not show you anything. It must be run under a load in the water. So, take the boat to the ramp. Take off the hood, and then take off the the plastic intake cover that goes over the carb. Now comes the trick part. Start getting it on plane to the time where it starts running weird then carefully cover half to 3/4 of the carb with your hand(as in your trying to cover the carb throat) all your doing is choking the motor. If it bogs even worse its not the carb, if it picks up it is your carb. I it seems to run perfect and idle perfect on the hose then bog at mid/ throttle under load its got to be a mid range curcuit or the high speed jets clogged. Thats it. Like i said the small motor carbs have very small jets and passages. Im really not trying to tell you , that you didnt do a good enough carb job, just merely helping you as i am a yamaha tech for a living


----------



## AfterHours2

Thx cut runner and brett for the help. Once Im home today I will try everything mentioned and hopefully come to a final verdict. I just want my speed back...


----------



## firecat1981

I was just skimming over this topic and I may have missed it, but what RPM's does your tach say you are running? If you don't have a tach then you won't know where you are.

I have a 20hp yamaha 4-stroke. When I bought it, after breaking it in, I swore it was only at like 3500 rpm's at WOT on the water and convinced I needed a different prop or it wasn't tuned right ot something. I bought a tiny tach and it turned out the motor was at like 5500 rpm's, exactly where it should be. It just sounded so different running under load then it did sitting static. 

Basically I'm saying there might not be anything wrong, But you won't know until you check the RPm's. I don't know what boat you are pushing with it, but remember it's a small motor and won't be a speed deamon.


----------



## AfterHours2

When I re prop the motor I probably will get a tiny tach and put it on there. I wish there wasn't anything wrong with it and it was just me but thats just a dream. The motor is on a highsider and should push it along nicely. Just got to get home and break out the drawing board again.


----------



## AfterHours2

One word "SeaFoam". I ran a whole pint in my 3 gal. and it not only cleared the jet that was clogged but also made the throttle more responsive than ever. Best $10 I ever spent...


----------



## firecat1981

Good deal, I always! run an additive in my boat tank, keeps things running nice. Usually Startron, but seafoam will work too.


----------



## AfterHours2

Well after a few runs the motor seems to be doing the same thing. I bought a rebuild kit, installed and cleaned the carb and jets today and took it out. The motor actually ran worse. Im just running in circles as to what this motor might need. Could it possibly be a problem with the lower unit? It runs fine on the ear muffs in the driveway but only acts up when it is put under a load in the water. This thing is driving me crazy and any help would be appreciated. Thx


----------



## Brett

When an outboard acts up, it can be the most frustrating thing to deal with.
But the rules are simple...Air, fuel, spark, timing, compression, cooling, lubrication.
Any of the items listed above can affect how your outboard runs.

My outboards are carbed and my trouble shooting routine is this:

Check the kill switch...make sure it's not activated.
Verify the vent is open on the tank.
Quick visual check for spark at plugs, condition of plug tips. Clean if covered in crud.
Drain fuel tank, check for contamination by dirt or water.
Verify interior of fuel tank is clean, including pickup screen.
Air leaks between the tank and pump have to be eliminated.
That means every fitting from pickup tube to the fuel pump has to be inspected and tested.
Brittle or cracking fuel hose and primer bulb means time to replace.
O-rings in connectors may need replacing.
Verify hose integrity from connector to fuel pump, including last-chance filter.
Clean or replace fuel filters, check water separator.
Pressure test fuel pump to verify function.
Verify hose integrity between pump and carb.
Hoses under the cowl are exposed to heat-vibration and get brittle. Replace if needed.
Check intake vacuum pressure.
Check integrity of scavenger tube from crankcase.
A cracked or broken tube changes the fuel/air ratio.
Rebuild carb, verify every passage is clean and clear.
Sometimes bits of metal from the machining process make it into the carb.
Solvents won't remove those bits from the idle passageways.
A manual/visual inspection has to be done to ensure a true and complete cleaning has been done.
Replace the carb float, don't keep using the old one, they do leak and lose buoyancy.
Replace float valve and valve seat, vibrations will change the shape of the tip and seat, they won't seal properly.
After reassembling carb and installing, check linkages and throttle sychronization.
Verify choke settings and idle settings.
Run compression test.
Replace spark plugs, one of the easiest things to do to make an outboard run better.
Plugs don't last forever, recommended replacement is after 300 hours of use or 3 years, max.
Replace spark plug wires at 5 years due to resistance build up and cracking of insulation.
Run outboard at night with cowl off, check for visible sparks, including from under flywheel.
Check spark with a spark gap tester, easy to buy or make one.
Obtain a volt-ohm meter and learn to use it.
Use the meter to test the ignition components, specs are in the OEM manual.
Coils, CDI controllers, sensors, stators have specific resistance readings at each wire connection.
if readings are outside OEM manual parameters, replace.
On older outboards, check ignition timing.
Check throttle cables for fit. Any play or looseness can result in low rpms on the water.
Ensure proper oil levels are maintained in 4 strokes, proper mix in 2 strokes.
Check water pressure exiting block, check thermostat, poppet valve.
Check engine overheat sensor. (again, info in OEM manual )

Lots of steps there, but it's what I have to do sometimes
in order to find the problem...or in some cases, problems.

                                    :'(



New outboards have brain boxes that record engine data
and that info can be read by a computer connection.
I'm not looking forward to having to buy that software.


----------



## twitch

Did you soak the carbs in carb dip or just spray the passages with carb cleaner?

Soaking them over night in the dip works much better than a couple of squirts of carb cleaner in a can.


----------



## firecat1981

Just curious, do you have a water seperator installed?


----------



## flyfshrmn82

I second the fuel additive comments. Also, not all two stroke oils are the same. Take it from me. I have torn my 15 yami 2stk engine apart 3 times after running 3 different oils. The oil I ran through my engine first (west marine) left a *very* stick film in my engine. I switched to Yamalube and ran for 50+hours then took back apart to inspect. Thin, shinny, happy and clean running little engine now.


----------



## DuckNut

Two things I picked up on and my wild azz guess.:



> When I  re prop the motor





> Its odd because it only happens when you put a load on the motor. Ive pretty much done all the basic fixes to the motor and now Im scratching my head on this one. Could it possibly be something in the lower unit. When you hammer the throttle down it is very sluggish and eventually picks up speed later


If you have too much pitch on that small of motor, they typically act this way.  The engine sounds fine in the driveway, runs smooth at idle and slow speeds in the water but does not have the muscle to push the water through the blades at speed.  Also, a SS prop is significantly heavier than aluminum and putting one of the same size and pitch as aluminum will affect the performance.

That's the extent of my helpfulness to you


----------



## AfterHours2

Well, after hours of testing, cleaning and using language Im not really fond of I have come to a final conclusion on the motor. Ethenol is a terrible thing. I ended up buying a new tank and fuel line and filled it with ethenol free gas and the motor now runs like it should or better. I also took some friendly advice and switched to yamaha oil. In the future, if Im not going to use the boat I will either donate the fuel to the lawn man or use for yard work. Thanks to all for the suggestions and kind help. I knew it had to be something simple but didn't think it was that easy. Thx again fellas.


----------



## AfterHours2

One more thing, Firecat brought up a good point regarding a fuel/water seperator. I know I do not have one installed between the tank and motor but there is a small clear filter inside the cowling behind the carb. Could this be it or is it a plain fuel filter. If it is not then what would you think the best way to go about installing one would be? Thx again!


----------



## Flpt

Glad you got it fixed. Had a similar problem with a yamaha once. Turns out the fuel line connector at the gas tank was cracked. It was a very small crack in the plastic threaded portion of the connector where the brass fuel line fitting screwed in. No problems until under load, then the motor would bog down.


----------



## Brett

> there is a small clear filter inside the cowling


That's the last chance filter, nothing more than a screen to keep chunks out of the carb and fuel pump.
A fuel water separator is a screw on canister with a filter element and trap.


http://www.boatingmag.com/maintenance/diy-projects/installing-fuelwater-separator


----------



## AfterHours2

Hate to bring this topic back from the grave but needless to say the motor went back to its normal problem of not running under a load. The whole fuel/carb issue has been eliminated with a new carb, fuel tank, hose & fittings and non ethanol gas. Just ordered a new CDI for the motor suspecting/hoping this will fix my ongoing problem. Compression is perfect at 120 in each cylinder but my top plug appears it is not firing correctly and the bottom is perfect. Hope this works so wish me luck. Anyone had a similar problem where a new CDI fixed the issue. This is my last resort before sending it to the shop but atleast I have given it a valient effort... Thx!


----------



## twitch

I think your money would have been better spent on a factory manual and a good volt/ohm meter. Testing electrical parts is way cheaper than replacing electrical/ignition components at random. IMO


----------



## cutrunner

A brand new carb? Really? Why? Hate to say it but twitch is right. After all the money you spent i think a good honest shop coulda fixed it for less.


----------



## firecat1981

Have you tried a different prop? Maybe the hub is bad on yours and starting to slip at higher RPM?


----------



## AfterHours2

Cut: The carb was actually a gimme that a buddy had and owed me a few peso's. But yes, they are expensive and I would not of spent the almost $200 to find out otherwise.

Firecat: New prop, same pitch is being used now so I guess I have ruled that out also. 

Many of the things I have replaced are considered maintenance items including tank, lines etc. With the exception of the CDI ($125.00) I do not feel I have spent a whole lot of $ on repairs. Most people replace and or rebuild these parts at a given time eventually so atleast I will not have to deal with them any time soon. Hope the CDI works....


----------



## firecat1981

Just curious what size and pitch the prop is? Also not sure if it has been asked, but how is it mounted on the boat? has it been moved at all?


----------



## AfterHours2

The prop is the original 9 pitch that came on the boat but new. The motor has never been moved from its location on the transom. It gave me a good year of worry free issues. Then it gradually started having problems off and on. As of now the issue is permanent and has not changed....


----------



## AfterHours2

Well needless to say the motor has been in a certified yami shop for over a month and the tech is still scratching his head on this one.. Compression good, spark good, everything ohms out properly to specs, carb tore apart and cleaned for probably 10th time and the motor still will not run under load.. As the motor sits, it should be running perfect but there is still something wrong... Any opinions from Yami guru's out there? Also, when you research the model # on the motor it comes back as not existant.. Possible international yami? I have no clue with this thing and every aspect of the motor seems quite odd to me.. Thx


----------



## cutrunner

Geez.. Nobody likes a problem like this. If you have good spark, know in your min that the carb is right, and have good air,and all the electical is right, i would start looking at a possible bad exhaust tuner or base gasket.. Something along those lines


----------



## AfterHours2

Thx for the response Cut.. It's been really hard for him to spend a lot of time continuously on the motor being slammed with work all the time. Plus, he is trying to avoid having an hourly bill at the end worth more than the motor.. It's just one of those things he says comes in from time to time and I will surely give him your suggestions... Thx again!


----------



## cutrunner

No problem. I know how he feels, we do a service on a 9.9 and it cost more than the motor at $110 an hour.. Its also funny cuz the little motors are almost harder to troubleshoot cuz everything is more finicky than a big motor. Just ask your mechanic if hes checking all the electrical "loaded and unloaded" to be sure. Again , yamahas electical is 2nd to none, and its almost never the problem. Reason i think it "maybe" an exhaust tuner or base gasket is because when the motors in the water that whole cavity fills up unlike when its on land on the ear muffs. What year is the motor?


----------



## Creek Runner

After hours where are you located? If you are close to Jacksonville bring me your engine and I will fix it (labor cost) for free; just because I want to see what's wrong with it. I am a certified master Yamaha technician.


----------



## AfterHours2

Creek- Im located in Orlando and if the problem is not solved then I will surely hit you up on the offer. Im headed up that way next month so I'll PM you if it looks like I need your help. Thx

Cut- The motor is an 03 and I don't think he has a test tank to check but instead takes it to the lake for test runs. Maybe it is something overlooked? Not sure as of yet but it is looking more towards being sold as a parts motor before the labor becomes more than the motor is worth. :'(


----------



## Creek Runner

Cut Runner, sense you’re a Yami tech to! Just wanted to bounce a couple things off you for this guy if that’s ok. If when he changed the fuel tank, hose, and primer bulb, etc. It ran good do you think that the exhaust tuner or base gasket would intermit like that?

I guess I should ask how many times, and for how long did it run good for? Also is the motor acting up the same way as before? Wondering if it’s the same problem or a new issue?

When you said that the top spark plugged looked like it wasn’t firing describe what you saw?
Was the plug black? Was it white or tan? Was it clean and soaked with fuel? 

Let’s assume it’s the same issue as before the only thing that would really cause an intermitting problem is trash moving around in the carb and or a electrical component breaking down under a load.  

Did you put a new CDI on it?

If I was working on the engine I would put a brand new set of plugs in it, run it under a load and then stop the engine and yank the plugs out. Spark plugs can tell you so much as to what’s going on with an engine.

Cut Runner feel free to chime in here since neither of us has the engine to diagnosis, maybe if we can come up with a conclusion together.


----------



## cutrunner

Ok, good plan. He said the problem stayed the same even with a completely different carb. Your right about the chance of an intermitent base gasket or tuner, not likely to happen... Also, he sayes hes changed the plugs and hes running factory ngks, and he has spark in both cylinders. Good spark, we dont know for sure. Ahh. Heres a shot in the dark, but kindof explains every syptom. Loose ground? Laugh, but its really worth a try. We had an f115 that had it. Tried every thing first (not me)


----------



## Creek Runner

Yeah I was kind of thinking a loose ground to, just seems it would have been caught by now.  I still think the best test now would be some old school things. 

I say run the engine in the water, with a brand new set of plugs. Try to idle for as little as possible since it runs good at idle. Open her up, then shut her down and yank the plugs, by reading the plugs we have a tell tell sign of what the issue is.

If the top plugs is fouled with gas and the bottom seems to be burning good (just using that because of a previous post). Well then we now have the problem limited to the top cylinder. And also have eliminated with almost all certainty that it’s not a fuel issue. And since we know we have good compression we have an electrical issue. So what controls the firing on the engine? It all starts with the Flywheel, then the Stator, CDI, Coil, and the spark plug.  So here is what I would do, I would swap the coils from the top and bottom cylinder. Then re-test if the problems moves to the bottom cyclinder then it’s your coil if it stays the same we have eliminated the coils all together. Which really only leaves the CDI since, if it were the stator typically it would just go bad and the motor would not start due to no spark.

Also the fact that the motor ran good after switching the fuel tank, primer bulb, etc. etc. Bugs me and leads me to believe that we have new issue.  After Hours chime in here and answer my questions in my previous post.

Also you could run her in the water open her up and the pull the plug wires off 1 at a time while running, this is the old school way of doing a drop test. Your testing to see if when you pull the plug wires the motor drops a cyclinder.


----------



## cutrunner

^ x2


We also need more info


----------



## AfterHours2

Sorry for the delay guys and I appreciate all the thought that has been going on while I was away. I actually replaced the CDI already to find out the problem was still there. The mechanic says he has already ohm'ed out the electrical side and everything was to the factory spec. I thought the problem was solved when I went through the fuel system and it ran good for a while on the lake but a trip later that day seemed to prove me wrong. The problem basically started out with it only bogging down every so often then progressed to doing it all the time. When I did pull the plugs the top cylinder plug looked like it was black/oily and the bottom had a nice brown look to it. I explained my findings to the best of my knowledge to the mechanic and he said everything had checked out ok on the electrical side and I have even concluded that both cylinders were properly firing with a spark tester and pulling the wires while running test. I'm going to give it another week or so then I might just pick the motor up. Like I said earlier, he is just working on it a few minutes here and there when he gets time so he can avoid giving me a bill for an absurd amount of hours and thats ok with me. He thought he may have had it when he did find a semi corroded ground but he fixed that issue and it still did the same thing. One of the hardest things about working on this problem is that everytime you fix something you think may be the problem then you have to wet test it at the lake. Its just takes a lot of time and I really do appreciate you guys using your expertise and I surely will bring up all of your ideas to him when I see him next. I just do not want to be a nuisance because he is the professional and some people do not really like others to tell them how to work on something when they are not in the same profession. Thx again guys for the help...


----------



## AfterHours2

Also, if one of you guys are interested in the used and still good CDI I took off the motor then let me know and I can ship it to you. Least I can do for all the help you have given me. First come first serve and it should save someone with a bad CDI about $150 or so. Just let me know.. Thx again...


----------



## cutrunner

Well, if it DOES have spark than you have a fuel issue


----------



## cutrunner

Again


----------



## Creek Runner

Did he pull the plug wires while under way or just at idle?
If the plug was black and oily that means it is firing and getting fuel. The black mean its firing and burning, the oily part tells me it may be getting to much fuel, assuming that it was a new plug.  

Have you checked the fuel pump? Have you inspected the reeds? I have another question in a previous post you stated that when you look up the serial number nothing comes up. So how are you ordering parts? How do you know the carb is the right carb since you replaced it? How long have you had the engine? Has it ever ran good?


----------



## cutrunner

Man, its too bad we cant see it in person, i wanna know. Mystery problens are hard ebough to diagnose, let alone without seeing it.


----------



## Creek Runner

Okay here what I can tell you for sure! If everything checks and is in good working order then it would run good. So either you’re missing something or in fact that everything with the fuel and electrical system is good. If we discount the fact that it ran good for a brief time and take in account that it has gotten worse I would say it’s time to look inside. If you are sure that all the test have been performed correctly. 

Cut it's been a while since I have worked on a Yamaha that small, Are the magnets internal?


----------



## cutrunner

Lol i havent touched anything smaller than a 250 since kennesaw last november. Round here in palm beach its all f350s.. I can check on my 25 2 stroke, or just look it up. Im with u on the fact that i fuel and electrical all check out than it must be internal, but.. I learned a long time ago to never trust anyone elses (that you dont know) diagnosis , write it off and try something else. No offense to whoever is working on it. Ive been biten hard for taking someones word.. :-[


----------



## Creek Runner

> I learned a long time ago to never trust anyone elses (that you dont know) diagnosis , write it off and try something else. No offense to whoever is working on it. Ive been biten hard for taking someones word..  :-[



Me too!!!


----------



## AfterHours2

Little update, stopped by the shop today to see how the progress was going and the motor was torn apart. Ends up, there was a small spot of JB weld on the block that ended up being corrosion all the way through allowing water in the exhaust? Exhaust ports were semi clogged and I could see the corrosion more clearly throughout. Could this be the problem? Don't know until the motor is reassembled.. Also, when the head was removed, normally the back side of the head at the cylinders area should be black but instead they looked like they were pretty clean and have been blasted with water. No water was present when the plugs were pulled so that is still a little of a mystery. Overall, I've taken it this far and with a few gaskets and the main cost going to a new reed valve assembly its better to know I have a sound motor in the end, hopefully..


----------



## AfterHours2

Also, the reason for replacing the reed assembly was that there was a gasket on it that was deteriorated when removed and apparently this is something that is not replacable unless the whole part is purchased. Any ideas or positives as to these problems being the culprit? Thx again guys for all the help....


----------



## cutrunner

Could be.. Still hard to tell without seeing it. Sounds like your guys on the right track


----------



## Frank_Sebastian

I have been repairing outboards for my family and friends for a long time. I consider myself an experienced amateur. (mostly bad experiences) In the past five or six years I have worked on two 9.9 four strokes and one 15 plus several 25 HPs. Some of the carbs are very hard to get right. Make sure the float is good and sitting at the proper angle. 

What I have done is clean the carb for as good as possible in regular cleaning bath. Rinse well and blow out with 100# air. Then soak at least overnight in engine tuner. I buy it by the gallon and sometimes leave problem ones 48 hours. Then 30 minutes in a heated ultra-sound bath. If you are careful and replace the needle just like it came out, it just might run. If not it must be somewhere else. I got all but one to run okay. One of the older ones was still less than it should be, but a new carb made it run right again. 
This is why I am not convinced it might still be the carburetor.

Best regards,
Frank_S


----------



## AfterHours2

Thx for the info Frank but the carb has had it's fair share of hands cleaning it over and over. I have even tried a new carb to find it doing the same thing. Hopefully after the motor is reassembled then the problem is resolved. If not, another motor may be in my future for this one has been exhausting....


----------

