Yamaha MR1 powered 2003 fx140 IDLES ROUGH but runs well after 3k. HELP!

[Zhaef]

Just recently purchased a 300 hr 03 fx140 for my family hoping to end up with a reliable top ofthe gas and go to the lake kind of ski. When I bought the ski it started right up but shook at idle and cleared up with some throttle. The original owner told me the motor mounts were broken and that was why he was selling it and why it shook so bad. I lifted on the motor and confirmed they were broken so I bought it.

Fast forward a couple weeks and I have done spark plugs out of good habit, replaced all 4 mounts, and changed oil. The motor still shakes pretty violently from idle to around 2800rpm. By 3000 the engine acts completely normal and that carries all the way to full throttle. I spent 2hrs run time on the lake this week and it ran well besides idle. Still starts right up I just won’t let it idle.

I read on this forum about all of the computer problems with the MR1 but that seems to be hanging an injector wide open? I don’t see that being my problem with how it runs anywhere but idle.

Do these have injector problems? I’m wondering if one is dripping while idling but is less noticeable with rpm? I’m still trying to figure out how to get the TB set off to check that.

I plan to do a compression check as well but the starter motor sounds very consistent when turning over so I didn’t really think much about compression.

Where do I begin? This seems to be the most informed group of people about maintaining the MR1 and I’m hopeful I can get this one back to reliable operation!

 

[Scottintexas]

welcome to the group,

Update your profile with your location so we know where you are at,

Does it run rough on the hose or only in the water ?

I might suggest removing the impeller/shaft to help isolate exactly where it's coming from,

Also, you may consider buying a YDS diagnostic unit to watch the engine real time on the computer to help diagnose the issue,



.

 

[Zhaef]

Idles rough everywhere. Runs out smooth beyond 3k everywhere. I’ve heard of the software just haven’t looked much into it yet. Thanks.

 

[ripler]

Software link

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[Seadeals]

Wondering if you have a problem with one cylinder. Once you hit 3000rpm it can feel “smooth” since the crankshaft has momentum and you don’t feel the missing cylinder anymore. I would definitely take compressions to know vitals. YDS lets you test fire injectors and read other sensor outputs in real-time running and not.

 

[Zhaef]

Cold compression test performed tonight. All 4 plugs were dark and wet. I could not figure out how to disable the injectors easily so I unplugged the fuel pump before cranking. The last 3 plugs may have been wet from remaining fuel pressure?

192 196 195 195 from front to rear. Now I think I want to remove the throttle bodies.

 

[Zhaef]

Loosened the throttle bodies and turned them upside down while still being fed fuel. Upon cranking they all 4 spray fairly similarly and none are stuck open. I also don’t see any leakage once I stop cranking.

No check engine light in the 2.5 hours I’ve run it. Anyone have any idea of where to start? Vacuum lines seem alright. Very hard to know for sure though.

 

[WREKS]

Did you check the coupler clearance when you replaced the motor mounts? Also, is their any free play in the drive line of the jet pump. The motor would have to be loose and slid forward to check this.

 

[Robb235]

@Zhaef, did you ever figure out your issue? I'm having a similar problem. Below 3k or so, the motor acts like it's running on three cylinders. But give it some throttle, and it runs smooth and has no problem reaching 11k RPMs. When I hooked up YDS, deactivating one cylinder at a time revealed that cylinder #3 doesn't seem to be firing at idle (engine speed didn't change when cylinder #3 was deactivated). But considering that the motor can reach max RPMs, it seems that cylinder #3 comes alive when given some throttle.

 

[Scottintexas]

MR1's are extremely sensitive about spark plugs and #3 has a known history of becoming rusted in place so be careful when you remove it,

If I had an idle issue (which I've had) the first thing I would do is change spark plugs,