[quote I'm not sure I know how it would blow up the crankcase..... There is no ignition source in the crankcase....

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You evidently have not been around much to not have seen the results of even having a large crankcase explosion from fumes gathered in the crankcase from just having a flooded engine.
A little of those gases that you are using to find the leak leak by the rings into a firing cylinder won't explode??? Well tell that to the guys that have had ballooned oil pans from nothing more than gas fumes built up from a flooded engine that fuel had leaked past the rings on. Oh well do as you please - but hope that you have good insurance.