Suzuki DF90 2004 Running Rich

[Mickeydee]

Hey all, just serviced my DF90…new powerhead anodes (4x), oil and filter, low pressure fuel filter, dropped the lower leg for new impeller and regrease shafts etc. Basically a good going over.
Was going to replace the spark plugs, when pulled them they are quite fouled up (black) from running rich. The engine seems to hesitate a little when lifting the throttle lever as well, which I suspect is due to the fuel mixture.
The service manual states that an O2 sensor can be connected for the ECM to recalibrate the fuel mixture. Before taking it into a dealer to discuss, what other things should I check or clean? I’ve looked at the map sensor and it appeared very clean. Removed the silencer and cleaned the throttle body some as there was some oil films and grime. The idle air valve is sucking in air as per what I think is normal. Not too sure what else I should check, so appreciate any of your input. And happy to provide further details if I haven’t described everything here.

oh and there doesn’t seem to be any exhaust leaking issue from corrosion that is common on this era engine.
Thanks all, Mickeydee

[Moonlighter]

As far as I know the 2004 DF90 doesnt have an O2 sensor.

If you meant to say a 2014 DF90A then that may be a different story.

was your fuel fresh?

[Mickeydee]

Its a 2004 model which doesn't have the O2 sensor. In the manual it says that a dealer can connect an O2 temporarily for the ECM to self adjust as the engine ages and components wear. Not sure how common place this procedure is or how significant a change it would make.

Fuel wise, we have a 100L tank which has not been fully emptied for a long time, but we keep it topped up full to minimise airspace. Within the last few months have used down to half way and filled up again. I could run the engine off a separate small tank of fuel straight from the pump.

We have used 98 octane fuel on a few occasions and I have since heard that we should stick to 95 to ensure we avoid alcohol content in the fuel. Not sure if this would cause the rich running/fouling of plugs.