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Went to pick up my bike from the dealer after its 20 hour service was performed. The tech changed out the spark plug noting excessive carbon fouling for only 22 hours. They gave me the plug back and recommended to just check it at the next service to see if it continues. This bike has basically taken 3 trips where it was ridden for several hours. I don't flog my bikes but I also don't let the bikes sit idling for long periods of time. The last ride was a colder day and I felt like the bike was using excessive fuel. Anyone else had issues like this with honda's fuel injected engines? I know its under warranty but I don't like sitting around waiting for the "broke" scenario so I ordered a ect sensor and o2 sensor with the idea that maybe its holding choke on with a misleading temp value or something with the o2. The only other thing I can think of would be to replace the injector. This was being run on 90 octane ethanol free fuel I drive over an hour to get (here in illinois almost all gas has 10% ethanol). The other note was that the intake valve was slightly out of spec on the loose side.

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Went to pick up my bike from the dealer after its 20 hour service was performed. The tech changed out the spark plug noting excessive carbon fouling for only 22 hours. They gave me the plug back and recommended to just check it at the next service to see if it continues. This bike has basically taken 3 trips where it was ridden for several hours. I don't flog my bikes but I also don't let the bikes sit idling for long periods of time. The last ride was a colder day and I felt like the bike was using excessive fuel. Anyone else had issues like this with honda's fuel injected engines? I know its under warranty but I don't like sitting around waiting for the "broke" scenario so I ordered a ect sensor and o2 sensor with the idea that maybe its holding choke on with a misleading temp value or something with the o2. The only other thing I can think of would be to replace the injector. This was being run on 90 octane ethanol free fuel I drive over an hour to get (here in illinois almost all gas has 10% ethanol). The other note was that the intake valve was slightly out of spec on the loose side.

View attachment 49602
The thing that is the toughest on spark plugs and O2 sensors on any fuel injected engine is frequent engine shut offs right away after initial cold start ups. The engine needs idle time or actual operation time to burn off the excess fuel required for cold start up. I always let my machine idle for a few minutes after a cold start up, even if I it was just to move it out of the way and it's 70 degrees outside. If you trailer it somewhere, don't just start up, back off the trailer, and then shut it off immediately. That's a guaranteed way to get a plug that looks like the pic and probably end up needing a new O2 sensor later on. Let it idle for a few minutes. These engines are designed to be able to idle a long time so no worries there. Now just run the dang thing and quit looking at the plug! (y)
 

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Discussion Starter #3
I wonder if being a 2020 model bought late in 2020 if some of the deposits would have been the dealer moving it around over the last year. Maybe too carboned up for the riding to clean up. Time will tell. I have '15 rancher 420 and weather permitting (probably next spring since winter is setting in) I am going to top off the tank on it and this 520 and put a new spark plug in each and then have the wife ride one and take them down one of the long smooth trails in wisconsin (cheese country trail). Then compare the results. I will leave both dct's in auto to make it as close as possible. I should be able to do a plug pull afterwards and see if the two look similar. Also compare how much fuel is used up and see if there is a significant difference.
 

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Though I’d prefer to see it a bit lighter, there is some tan showing on the insulator and center electrode. For a new engine with rings breaking in I don’t see it as that bad, especially if you haven’t been running at high speeds/loads or if you’ve been doing cold start/short run cycles.

If it were mine I’d make sure to keep the air filter clean and not over-oiled, run it reasonably hard, and see what it looks like at the next service.
 
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