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Engine stutter.

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pwwalden

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I have 2004 RL 251 with the 350 MPI. Just a few minutes ago the boat has started studdering at full throttle. I'm thinking full filter? Please help.
 
Could be lots of things besides fuel but that tends to be the typical solution.

Filters - both the fuel/water separator and any others on the engine itself. I'm not familiar with an inboard Merc but the Yamaha OB's have several extra filters on the engine itself.

Tank vents - cogged vents will lead to the fuel pumps not being able to pull enough fuel at higher RPMs, typically you will see this in a fuel bulb sucking flat. But an IB engine may not have that.

Air leaks - bad/old fuel lines or improper maintenance (seals/gaskets not tight) can lead to air being sucked in the fuel delivery and cause issues. Sometimes fuel lines that are old can delaminate internally and cause blockages.

Fuel pickup - blocked by debris in the tank

Bad fuel - phase separated

There are dozens of points of failure so I would recommend doing a search on a site like The Hull Truth where there are multiple times more users and advice than a boat-specific site. Example below.

Good luck!

 
Perhaps you're hitting the rev limiter.
TT
 
pwwalden said:
I have 2004 RL 251 with the 350 MPI. Just a few minutes ago the boat has started studdering at full throttle. I'm thinking full filter? Please help.
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I had a 2004 Mercruiser 4.3L V6 I/O. Does it also stutter at idle?!? One year I didn't change my fuel/water separator. Well it started to run like crap/stutter as you put it. Once I changed the filter and ran some seafoam through it it slowly burned through the watery fuel..... it ran fine!!!
 
High jacking this thread, lol…. Had this issue on my new 2022 24 LSB, SPS+ w Yamaha 250 SHO.

Had no idea what was going on, but started with ROM dropping out when trying to go full throttle, but ok at 4500 and lower…. Later in they day after tubing a bit, started losing throttle(drop outs) at 3500RPM and lower…. Noticed when pulling the kids in that the primer bulb was sucked flat, so I know it’s a fuel flow issue.

I can’t imagine it’s the fuel/water separator, but I can check it I suppose. Where are the vents and how should I check them for the tank? Any other things I should check? 43 hours on. The motor, and just had the break in service about 10 hours ago….

Thanks!
 
jcr159 said:
High jacking this thread, lol…. Had this issue on my new 2022 24 LSB, SPS+ w Yamaha 250 SHO.

Had no idea what was going on, but started with ROM dropping out when trying to go full throttle, but ok at 4500 and lower…. Later in they day after tubing a bit, started losing throttle(drop outs) at 3500RPM and lower…. Noticed when pulling the kids in that the primer bulb was sucked flat, so I know it’s a fuel flow issue.

I can’t imagine it’s the fuel/water separator, but I can check it I suppose. Where are the vents and how should I check them for the tank? Any other things I should check? 43 hours on. The motor, and just had the break in service about 10 hours ago….

Thanks!
Click to expand...
Your 250 SHO should also set off an alarm and go into limp mode if it is a fuel water seperator issue. There is a sensor in those filter/seperators. That would make me also lean towards it being a different issue if you don’t have the alarm and limp mode happening.
 
Vikingstaff said:
Your 250 SHO should also set off an alarm and go into limp mode if it is a fuel water seperator issue. There is a sensor in those filter/seperators. That would make me also lean towards it being a different issue if you don’t have the alarm and limp mode happening.
Click to expand...
Definitely didn’t hear an alarm…. Seems like a venting issue hopefully. I’ll probably replace/empty the filter just to check it anyway.

Advice or links to the venting system diagrams and troubleshooting?
 
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