DT60 runs rough

Thanks for the opportunity to post here, this is my first post. We have a 2000 Suz DT60 with 1100 hours and a good history, good compression. It starts fine and handles lower idle speeds, but then runs rough between 2000-3000 rpms, and will not exceed 3000 rpms unless in reverse, where it seems to run normal or at least the tach will go to 4000 rpm (which sounds weird). We've replaced the plugs, injectors, low pressure fuel pump, fuel filters. We've inspected the fuel tank, fuel vent on tank, fuel line leaving the tank and the uptake screen on tank line. After running yesterday for an hour at 2000 rpm, the plugs had some excess gas on them, which then made me think it was getting fuel, just not handling properly. Wondering if the fuel vapor separator, which I know next to nothing about, is a likely place to look. Also, wondering if there are some sensors that might be impacting. We have check the neutral over-idle sensor for mechanical function, have not checked it for continuity. It is does not appear to stick. I appreciate any thoughts you might have.

Firstly, don't you mean a DF60, Suzuki never made a fuel injected DT60? The reason you get higher RPM in reverse is because there is a lot less thrust and therefore less load.Try and identify if one or more cylinders are misfiring. Check that your thermostat is not stuck open because that will cause the engine to run very cold and very rich which will foul the spark plugs. If all is okay there, check to see if your temp sensor is operating using an ohms meter and monitoring the resistance change as it warms up.Check fuel pressure is correct, Suzuki fuel pressure regulators are mounted in the bottom of the fuel bowl and have a tendency to corrode which causes them to fail.

Hi iang6766, I had attempted to thank you for this post right after you made it back in July. Want you to know I appreciate the thoughts and help!

No problem, did you sort it out?

iang6766 said:

No problem, did you sort it out?

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Life got busy in late July, and I'm just circling back. I replaced the thermostat, wasn't open, but cheap thing to do with this many hours on the unit. The temp sensor and fuel regulator are next, I guess. I'm not a boat mechanic, or even a good general mechanic. My guess is it is in the fuel bowl area, I've watched a couple videos of them being taken apart. It's on the edge of my competency, so not sure I'll dive in to that.

Thanks a ton for your support.