The water trick works.
A spray bottle is what I use also.
I didn't think a HP500 would get
carboned up either, til I was working
on a friends boat, I was dealing with a starting
issue, I had the coil wire off, cranked it over,
and it "dieseled", ( this boat is regulary flogged,
so, you wouldn't think it would have any carbon
build up) this was with the engine running on
the "hose" too, ( not that much engine heat )
I doubt the timing is going to cause any
issues,as far as the "dieseling"/run on
when shutting it off,
since the ignition is off, there should
be no spark.