bongo continues to run even when keys removed! - did a quick search and found out about the fuel solenoid issues

protocol for stopping engine - is this bad for the bongo engine?
I managed to stop the thing by blocking the entry air at the intake with a bit of stiff cardboard (easier than the exhaust) and switching the bongo to diesel with no diesel in the tank (running 2 tank system) - just wondered if this would do any harm to the bong stopping in this way.
I did block the intake and pressed the throttle and aload of black smoke came out which was quite alarming!! not done it since is this good, smelt bad!!!
Before i did that i removed the fuel sediment drain, but that causes an air lock problem that requires a purge hastle (pressing the top of the filter on turning the engine. I was surprised that neither method gave a quick stop to the engine!!! and wonder if they are doing any harm
Alternate explanaition
also a mechanic friend suggests it might be the ignition barrel and describes an electric switch that goes on the end of the barrel, might it be this? and if so what do i search for on ebay to get one?
I have ordered the bosch fuel solenoid that kirsty described in her other posts, but continue to drive the bong as it's my only car any feedback appreciated on what seems to be quite a common issue
rgds Paul