I signed up just to add to this thread, as this is one I followed when I had the same loss-of-power-issue.
I have a '21 850, witting around 1500 hours right now. I keep up on maintenance, although I'll have to admit I had been missing the pillow block bearing so good I was deep diving the issues.
I had no warning, buggy was running fine, but yesterday coming up the laneway, she lost all power. I could sit a moment, then it would go maybe 4 feet, then die. I could hear a hissing sound from the right side, I assumed that was the fuel cap.
Anyway, got it back to the garage, pulled off the air filters, coils and pulled the plugs. They had probably 500 hours on them, but they looked fine. Gapped and replaced them, cleaned out the boots and bolted everything back together. Air filters were new, but checked them anyway. No issue with inner or outer. Started it up, same thing, 4 feet, dead. Could rev the engine in neutral no problem, 3000-4000 RPM. But try and drive it, nope. I live in 99% pure dust, so I can't run these things without an air filter except in winter, or I would have tried that....
So I went and ran the numbers on some of the sensors, and THEY were all checking out. I pulled all of the breather hoses I could, just to check for obstructions, it just seemed like it was getting choked. Really looking, I saw that hard line that runs to the air filter box, coming in from the bottom. No real easy way to get that off there, so what the heck I stick a shop vac hose in there...
It sounds like it's fighting something, which isn't right for an air feed. I take a real good look at the air filter and there is a pink ring about the size of that air tube on the side of the outer filter, so I fashion a better seal on that tube and give er again with the vac. BOOMF. Just a mass of congealed packrat, a good sized one too. Had cemented itself just down the inlet so it wasn't visible at all. But there it was. Today I plan to follow that hard line and see where it gets air from, see if there isn't a way to screen that off as it's got to be pretty big to get a packrat in there (I absolutely hate packrats, that is the single most destructive animal we have here, and I'm in the deep deep woods). I will update when I get that figured out. Funny thing is I do recall catching the faint smell of "dead mouse" around the buggy but can't recall how long. I figured whatever it was would just dry itself out.
Sorry for the ramble, wanted to make the first post a doozy.
That said, for anyone looking at one of these...I read all the "deez are da crap, dey gots da subarus and dey all crap" posts, and look, EVERY buggy is going to have issues, we ride them hard, we work them hard. My experience (and I have NO affiliation to Kubota, I personally think their pricing is insane, but love their products) is this:
I have used this buggy to haul full loads of logs out of the forest, 15 full cords a year, and since I'm on a mountain, that's constant 10-30deg runs. I have a half mile laneway that has 7 switchbacks and a rise of 300'. We get up to 10' drifts of snow. I use the buggy with a plow on it to clear that driveway. I've pulled pickups and an old blazer around with it. I've gone mudding with it, I use the roof as a shooting rest. The thing has not had a single issue, nothing (well less packrat incursion). I DO keep up on all the maintenance, I DO use a bit of seafoam in the gas and in the crankcase (anyone who says it shouldn't be used in a crankcase quite literally doesn't know what they are talking about).
In fact, the only negative was the factory battery, it died in less than a year and the dealer didn't want to replace, but meh, I can live with that. Oh and the tires (in the pic) only lasted about 1000 hours, but again, ROUGH use. I ended up ordering those same ties, just upgraded the rims, because they worked on dust, mud and ice.
Anywhoo...hopefully this post is of help to anyone looking up the same issue, it does seem that inlet is a weak point, maybe I've lost a screen or something, that packrat was about a foot long. YES they are extremely flexible, but it shouldn't have been able to get in there.
I see a “lineup” of machines at my local dealer…haven’t stopped to see if what they are though.
