Temp is a factor yes. But not necessarily in the way you think. Air cooled engines run hotter than water cooled yes.... but not many people work these engines hard enough to keep the carbon burnt off. If you work them... I mean REALLY work them.... Like for 5 or 6 hours at a time under full load.... They don't carbon up near as bad. It's the ones that "put" around and don't get worked hard, (or only work hard for short times) that carbon up so fast.
Truth be told... car engines need it too. Anyone who has ever had the intake plenum off of a "newer" automotive engine has seen the horrible carbon build up that occurs in them. There is good reason why products like Sea Foam were created. (That's a plug for Sea Foam, I am not affiliated in any way, but it's really good stuff.)
More explanation:
Carbon on top of a piston gets hot when under load. If you work the engine hard enough, that carbon will get red hot. Red hot is hot enough to cause pre-ignition. (Pre-ignition: gas is ignited by another source besides the spark plug at the wrong time.) Pre-ignition can cause cylinder damage, hot spots, "pinging" and a other damaging things. The reason that Kohler recommends you to pull the head and clean it is for longevity. The reason car makers don't recommend it is for a couple reasons: It doesn't happen as quickly, or as often as it does on this smaller engine (for reasons already discussed). Secondly: It's just too costly. Seriously... who would pay a shop to pull the heads off a 350 Chevy just to clean it and reassemble it? NO ONE. But as someone whose taken apart a lot of those motors... they need it.
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