Once when bump-starting the GS, I forgot to turn-on the kill switch    .   The bike seemed to start, and fired maybe 4 times, then quit.  So the odd thing is: if the kill switch was set to OFF, how could the engine sputter during a bump-start?  I'd think that there is zero spark.  But I could have sworn that there were a few "putt-putt" sounds in there, as if the fuel was actually firing.

could it just have been air moving through the engine? The crank would have been turning, and the pistons would have been going up and down. This will produce a sort of "putt-putt" sound but it isn't as loud as when fuel is ignited.

The mixture can be ignited without spark under the correct circumstances. I don't know what the conditions needed for un-sparked ignition in a gasoline engine are, or whether a cold gs engine can create those conditions though.

On a side note, diesel engines work by using compression to ignite the mixture.

Its just the engine being driven by the rear wheel. Except for the exhaust noise, if you could tow your GS down the road in gear, it would sound like it was running (don't try it).

It sounds as though the "putt putt" sound I heard was probably just the air moving.

Regarding: being bad to tow a GS... other than being dangerous, would it be hard on the engine?  I'd think that oil would get circulated either way; maybe a problem with the unburnt fuel?

Like towing a car in gear... just dont tow it to 80 mph in first gear...
Cool.
Srinath.