I don't see how running it out of fuel will do any harm, even with a two stroke (I shut off as soon as the revs increase). My theory is is that varnish
and gunk inducing constituents in the fuel are best burnt off before they become varnish
or gunk. I have a Johnson 3.5 2 st that spends weeks at a time unused that I've just had to clean the carbi on, mainly because there was water
in the tank but I figured it was due for the full service
after 8 years untouched anyway. All I found was a little bit of crystalized gunk in the bottom of the float boal and very little varnish staining.
Small four stroke are more susceptible to problems with fuel because of their much finer jets then either corresponding 2 stroke
or bigger 4 st engines so it is possible that gunk in the jets could dry and harden and then require mechanical removal
. Having said that, I think the fuel in your average float bowl would evaporate within a couple of days anyway.