Greetings..new poster here with a perplexing problem that just occurred to my otherwise rock-solid and dependable Yamaha 15HP 2-stroke.
It's a 2007 model...15MSHG.
I'll preface this by saying that I am competent with tools and own two motorcycles which I service myself. When I can't figure something out, I usually look to forums for help, so I am hoping someone can help me now...here is the story, in a nutshell:
A week ago, we were headed towards our favorite fishing spot. Struck something in the water, small section of branch that felt as if we'd run over a fence post. Carried on as if nothing had happened. I doubt that this has anything to do with the problem that I will describe, but thought I should mention it nonetheless.
Fished for about an hour....motoring between hotspots; no problems.
When I moved to another location, I let the motor idle down, whereon it stalled and stopped.
No biggie, I thought, but when it came time to move, I couldn't get the engine started for love nor money.
Pulled and pulled and pulled....then checked fuel delivery...even pulled the spark plugs to check for fouling. No APPARENT cause for the dead engine.
After a half hour or so, I managed to get her going again, and we beat a hasty retreat back to camp. She ran like the wind all the way back, so I presumed that this incident was a "one off".
When we left to go out after dinner, she started easily enough...but then bogged down to almost nothing - even at full throttle - and eventually died. Needless to say, we called it a day.
Next day, I pulled the carb (I always carry a rebuild kit), suspecting a clogged port or jet. Upon dismantling the carb, I found nothing obvious...no grit...no chunks...no varnish or gunk to be seen - I usually run Seafoam in every tank. This was disconcerting because it meant there was no overt cause to this grief. I re-assembled and replaced the carb and she started on the first pull like she always had done before. Now although she ran like the wind at full throttle...it was obvious that low speed (and off-idle) was not normal; surging...sputtering...ran rough.
Fast forward to yesterday, when I perused all sorts of forums and YouTube videos regarding carb-rebuilding for this model. Realizing that I had missed the idle jet, I decided to open it up again tonight and do a more thorough job.
I pulled the main jet, needle jet and idle jet from their positions and checked each meticulously; all were clear. I soaked the carb body in cleaner/degreaser and blew compressed air through each port, passage and hole I could find. I also drilled out the plug for the idle mixture screw and checked the setting...it was completely bottomed-out....from the factory.
I also checked and cleaned out the fuel filter...nothing of note in there either.
I re-assembled the unit and refitted it to the engine that was in the testing tank. After priming the fuel bulb, it took MANY pulls before she finally started and then, she ran like crap.
I had to roll on the throttle fully, or she would die...it was as if she was starved for fuel. After running (badly) for a few minutes I thought I would try the mixture screw to see if it would make a difference. I turned it one full turn out and the engine ran remarkably better. The optimum setting is at about 1? turns from fully seated...which is strange because it WAS totally closed from the factory for the past ten years and ran fine! If I pull a spark plug lead while running, the engine reacts like an engine running on one cylinder...rough, but recovers when the lead is replaced. This is true for BOTH plugs, so I don't believe this is an ignition issue. Also, when running it in the tank, she doesn't rev up as well as she did in the past...but I realize this could just be an issue with linkages and such that weren't put back in exactly the same place as they were before.
If I disconnect the linkage (bypassing the throttle-stop) I can rev her up fairly well, but she bogs on quick acceleration. If I rev her up good...she will sometimes stumble to the point of stalling, when the throttle is released. Sometimes, but not always...which is even more frustrating when trying to troubleshoot!
At this point...I am totally stumped.
It's a 2007 model...15MSHG.
I'll preface this by saying that I am competent with tools and own two motorcycles which I service myself. When I can't figure something out, I usually look to forums for help, so I am hoping someone can help me now...here is the story, in a nutshell:
A week ago, we were headed towards our favorite fishing spot. Struck something in the water, small section of branch that felt as if we'd run over a fence post. Carried on as if nothing had happened. I doubt that this has anything to do with the problem that I will describe, but thought I should mention it nonetheless.
Fished for about an hour....motoring between hotspots; no problems.
When I moved to another location, I let the motor idle down, whereon it stalled and stopped.
No biggie, I thought, but when it came time to move, I couldn't get the engine started for love nor money.
Pulled and pulled and pulled....then checked fuel delivery...even pulled the spark plugs to check for fouling. No APPARENT cause for the dead engine.
After a half hour or so, I managed to get her going again, and we beat a hasty retreat back to camp. She ran like the wind all the way back, so I presumed that this incident was a "one off".
When we left to go out after dinner, she started easily enough...but then bogged down to almost nothing - even at full throttle - and eventually died. Needless to say, we called it a day.
Next day, I pulled the carb (I always carry a rebuild kit), suspecting a clogged port or jet. Upon dismantling the carb, I found nothing obvious...no grit...no chunks...no varnish or gunk to be seen - I usually run Seafoam in every tank. This was disconcerting because it meant there was no overt cause to this grief. I re-assembled and replaced the carb and she started on the first pull like she always had done before. Now although she ran like the wind at full throttle...it was obvious that low speed (and off-idle) was not normal; surging...sputtering...ran rough.
Fast forward to yesterday, when I perused all sorts of forums and YouTube videos regarding carb-rebuilding for this model. Realizing that I had missed the idle jet, I decided to open it up again tonight and do a more thorough job.
I pulled the main jet, needle jet and idle jet from their positions and checked each meticulously; all were clear. I soaked the carb body in cleaner/degreaser and blew compressed air through each port, passage and hole I could find. I also drilled out the plug for the idle mixture screw and checked the setting...it was completely bottomed-out....from the factory.
I also checked and cleaned out the fuel filter...nothing of note in there either.
I re-assembled the unit and refitted it to the engine that was in the testing tank. After priming the fuel bulb, it took MANY pulls before she finally started and then, she ran like crap.
I had to roll on the throttle fully, or she would die...it was as if she was starved for fuel. After running (badly) for a few minutes I thought I would try the mixture screw to see if it would make a difference. I turned it one full turn out and the engine ran remarkably better. The optimum setting is at about 1? turns from fully seated...which is strange because it WAS totally closed from the factory for the past ten years and ran fine! If I pull a spark plug lead while running, the engine reacts like an engine running on one cylinder...rough, but recovers when the lead is replaced. This is true for BOTH plugs, so I don't believe this is an ignition issue. Also, when running it in the tank, she doesn't rev up as well as she did in the past...but I realize this could just be an issue with linkages and such that weren't put back in exactly the same place as they were before.
If I disconnect the linkage (bypassing the throttle-stop) I can rev her up fairly well, but she bogs on quick acceleration. If I rev her up good...she will sometimes stumble to the point of stalling, when the throttle is released. Sometimes, but not always...which is even more frustrating when trying to troubleshoot!
At this point...I am totally stumped.
