Re: Honda Guy Here...
Gents, I would argue that it is a problems of physics BUT that's an engineering problem and Honda is responsible for the engineering in their products.
Honda would not be the first company that simply built a product without testing it in every possible environment. Apparently, when you have an engine of that size, and you design tiny carb jets in order to accomodate a small fuel flow, and then you add US market gasoline and the Arizona climate, you exceed the operating parameters of the engine.
That doesn't mean Honda is evil (that's reserved for Google) just that someone built an engine which is not suitable for that particular market. Perhaps it is a design problem, perhaps there are other ways to feed that size engine in that climate. Doesn't really matter unless you want to argue that Honda should take the engine back due to an inherent design defect.
What might be simpler, and certainly cheaper than chasing avgas, is just adding Sta-Bil or a similar gasoline stabilant to the fuel with (sadly) every filling. These products aren't just high end solvents, they are typically a naphtha base but with some enzymes or anti-oxidants or other "pinch of magic" dissolved in there.
And they've got a track record for preventing gumming and fuel breakdowns.
The other option is to disconnect the fuel (or is that an internal tank?) or do what you must to allow the engine to be RUN DRY after each use. That runs the gas out of the carb, typically preventing gumming in the passages.
Disappointing engineering, disappointing fuel. I wish I could buy pure gasoline for my car, ethanol is just throwing away money and since I burn about 10% more, it isn't really saving on emissions either.