Damn good idea with the Propane - does it run good enough to tell the difference though ? Just thinking when I used to run converter/mixer systems, when you changed from petrol to gas, you'd have that short interim period with the petrol/LPG mix, running would be pretty crappy.

Yes, a free flowing air filter like that is a hell of lot less restrictive to pressure buildup from a backfire, than an enclosed CAI.