Mmm, right, I had a waxing event today which may have led to some explanation of part of the stuff that's been going on. Although, not in the sense of why the waxing happens in the first place, but why the Honda seems to be immune to it.
It having been so dry lately, I resolved to run the tiller through the plots that had been forked over a few days ago. I decided to run through each plot twice and spread a bit of grass on before the second pass, so I can forget about the lawns for a bit. The Honda, on the tiller, ran perfectly, as it always does, but the Kawasaki, on the mower, waxed up on the last stripe (fortunately).
Whilst doing all this, I had time to consider the two situations - the Honda is a much smaller engine, which ought to make it more vulnerable, all things being equal - however, I realised that all things are not equal.
The machine that the Honda is mounted on was originally designed for a two-stroke motor, but the reason for using a two-stroke no longer applies and they have been fitting this far superior four-stroke one for many years now. However, they have left as much as possible of the old machine design just as it was - essentially, they just fit a different engine. They are still using the same fuel tank, and its mountings, just as they were back in the two-stroke days. This means that the tank is in such a position that it still needs the fuel pump arrangement that the two-stroke required. This pump is a diaphragm affair, driven by the induction pulses.
The Kawasaki on the mower simply relies on a gravity feed from a tank mounted a few inches above the carburettor.
It may be that the Honda survives the waxing for one of two reasons. Either the pump is sufficiently effective to 'blow' the wax through the jet orifice, or the constant pumping and recirculation keeps the wax in solution, or at least soft enough to be drawn through the jet - or both.
Not a lot I can do to use this 'knowledge', even if it is true, of course.