Yam 15 runs rough on start up

[yammie15]

Erratic RPM's - Yam15hp

Since new, this Yammie has never run as well as the one I bought back in 1993, but has been reliable.

Engine is a 2009 two stroke that I use daily as a dingy motor. Still starts well, choke and a couple of pulls in the morning, but sounds like a bucket of bolts on the way to the dock, a quarter of a mile away. It idles ok but if I shut down the fuel right after starting, I'll get a couple of misfires.

RPM's drop and rise slightly, enough for me to feel the dingy surging, but not so much anyone would notice who is watching.

The engine seems to rattle like something's loose and I thought it was the cowling because when I put my hand on it, things quieted down, but now I believe the sound is just reverberating through the cowling.

Changed plugs. Cleaned and changed fuel strainers. Stuck a piece of rag under the cowling.

I hardly ever run the engine above quarter-throttle; as indicated by the little bars on the grip. Never bring the dingy up on plane.

And, of course, when the engine warms up, all this seems to go away!

Does this thing just need a tune-up? Or is a bearing going?

No decent mechanics where I'm located so will have to do my own work. (And hopefully learn something.)

Would appreciate any ideas as to how to make this little baby sing!

Thanks,
Bry

[99yam40]

Not enough info to even guess what the problem is.

Post results of compression test, spark test, timing test
Post complete motor model #
Have you changed or checked fuel pump?
Have you cleaned the carb or even looked inside of it to see what you find in there?

Does this thing have a choke on it?

[yammie15]

Thanks for getting back to me. Appreciate it!

Yamaha 15MSH. Model #684KS1057789

And yes, it has a choke.

I'm living on a sailboat in a third world country and don't have access to even the simplest diagnostic tools. No compression gauge for example, so I can't supply the information you ask for. But I'm glad you asked... I'm behind the 8-Ball here and now know it! What do I need to add to my basic tool kit to analyze outboard engine problems?

The short answer to your other questions is: no. I bought the engine new and it has been satisfactory 'till now. I did get some water in the fuel recently and disassemble the fuel pump and fuel strainer. The fuel pump seems to operate normally, but how can I test it? I've never touched the carburetor. If this could be the problem, should I remove it from the engine? Then what?

Apologize if I sound inadequate, but no outboard mechanics here and I do want to learn.

Thank you, again...

Regards,
Bry

[robert graham]

On the bottom/side of the carburetor there should be a brass hex or slot head drain screw....drain the carb from time to time to remove water/debris to improve running...put a rag under the carb so when/if you drop the drain screw it doesn't drop down somewhere and get lost....the rag will also catch the fuel that you drain out so you can see any water/debris that might have been in that float chamber...

[99yam40]

Thanks for getting back to me. Appreciate it!

Yamaha 15MSH. Model #684KS1057789

And yes, it has a choke.

I'm living on a sailboat in a third world country and don't have access to even the simplest diagnostic tools. No compression gauge for example, so I can't supply the information you ask for. But I'm glad you asked... I'm behind the 8-Ball here and now know it! What do I need to add to my basic tool kit to analyze outboard engine problems?

The short answer to your other questions is: no. I bought the engine new and it has been satisfactory 'till now. I did get some water in the fuel recently and disassemble the fuel pump and fuel strainer. The fuel pump seems to operate normally, but how can I test it? I've never touched the carburetor. If this could be the problem, should I remove it from the engine? Then what?

Apologize if I sound inadequate, but no outboard mechanics here and I do want to learn.

Thank you, again...

Regards,
Bry

If there is something rattling around it could be bad, but hard to tell what is going on from what you have posted. Maybe it is missing real bad or has a lean sneeze..
A Yamaha service manual is something you should have if you plan on working on your motor, it has lots on info.

If you had water in fuel and you did not clean out the carb then I would think that would be the 1st thing to look into.

Of coarse if the cylinders are not sealing properly it would not be worth going much farther without fixing that 1st, That is why compression test or leak down test is good to do on any motor

[TownsendsFJR1300]

On the bottom/side of the carburetor there should be a brass hex or slot head drain screw....drain the carb from time to time to remove water/debris to improve running...put a rag under the carb so when/if you drop the drain screw it doesn't drop down somewhere and get lost....the rag will also catch the fuel that you drain out so you can see any water/debris that might have been in that float chamber...

Just to add to this, if you can use a small can/container (I use a tuna fish can) to catch what comes out would be very helpful. Any debris/ cludy fuel, etc. If debris comes out, prime the primer ball some more and flush out the carb until its clean.

Have you ever used any fuel cleaner in the engine? Yamaha makes a product called RingFree that ccleans the entire fuel system and top end of the engine. Excellent product and works extremly well (1oz / 10 galloins). You can run it at a heavier dose without any ill effects.


https://www.yamahapartsandaccessorie...?b=Search&d=34

[yammie15]

Thanks everyone. Sorry... took me awhile to get back to you... had to buy a tin of tuna!

Found the drain on the carb. It's a slotted screw on the side of the bowl, down low. Got fuel out and pumped the bulb for a quick flush. All seemed clean and no water bubbles. I don't have access to the Yamaha fuel additive but I do have Red Line Fuel System Cleaner, active ingredient is PEA detergent. Not sure if this is ok for use in a 2 cycle application, but will do some research on this before adding it to my gas tank.

Revs still inconsistent; more noticeable with a cold engine. Appreciate any other ideas and, besides a shop manual and compression gauge, what else should I order for my tool bag? I really rely on my outboard, to the point of thinking about buying a second, smaller one, so really want to feel confident about maintaining it.

Many thanks,
Bry

[robert graham]

You use it daily as a dingy/tender....so how old is that gas in the tank?....and do you use a fuel stabilizer like Stabil or similar?....maybe your gas has gotten old/stale.....

[yammie15]

Thanks, Robert:
I use the motor daily and go through about 3 gallons of fuel every two weeks so the gas is fresh. I don't use a fuel additive as a rule but maybe will try the RED LINE fuel system cleaner that I mentioned above.

Thanx,
Bry