DF9.9 runs, but seems to only be on one cylinder. Fuel? Ignition?

[onepyramid]

Took it out for the first time this year and it started right up and ran fine on the water for about five minutes. Then it started to falter, intermittently. I made it back to the dock, but it continues to run improperly, although now it is all the time, not intermittently.

I assumed maybe bad gas, so I flushed the tank and hose and refilled with non-ethanol fuel. Put that to the motor and have run it enough to have used up all that may have been left in the motor lines, pump, etc. I pulled the plugs and neither was fouled.

It will start now, but needs the fast idle lever up to get it to go. I will run at higher than idle speeds, but when returned to regular idle it will die. I've swapped ECM modules to make sure it was nothing in that and it runs poorly regardless of module.

Any ideas on where I should start looking next? Should I have done something to the fuel filter, or other fuel related pieces on the motor, itself? I really don't think it was bad gas, as the gas from the tank sat inside my garage of the winter, with Sta-Bil added...and I always use the premium no-ethanol gas.

Any and all help would be appreciated. Thanks.

[Murray]

Has a similar issue with a new to me Honda 9.9 that sat for 6 years. The previous owner would start it with fresh fuel every couple of months but never drained the carburetor and didn’t likely run it long enough to completely exchange the fuel in the carburetor so the carburetor started to gum up. Found Seafoam’s website and they suggested a 2:1 ratio of fuel to Seafoam. I fought with the engine to keep it running until it was up to operating temperature then let it sit for 72 hours. It now starts on the second pull and no more fooling with the choke to keep it running. I haven’t been able to test it on the water yet but I did notice a considerable improvement. Figured I try Seafoam before stripping the carburetor down and cleaning it which I may have to do anyways. If the ice would only leave the lake…

[onepyramid]

Sorry, I should have specified...this is a 2017 Suzuki with fuel injection.

[Murray]

Shouldn’t matter, carburetor or fuel injection will gum up with gas sitting in it over time. Think how small the injector ports are, smaller than the carburetor passages I’m sure. It’s just a suggestion that might help and it’s a simple fix(if it works). Somewhere on your full system there might be a drain, if you can find the drain then drain the fuel then introduce a mixture of injector cleaner and fresh fuel. I’ve had good luck with Seafood but there’s other products that will do the same. I do think your issue is fuel related, this is a common occurrence with seasonal small engines. I’ve been down this road enough times that I drain or run dry all the fuel out of carburetors that are going to sit for more than 3 weeks.
Can’t hurt to change fuel filter and spark plugs if they haven’t been done in a while. Start with the simple things.