They run fine inverted, tank location isn't important within reason bacause the system is pressurized. Don't have any 45's now, but had a pair a few years ago... yes they are a beast. One would think the regulator should keep fuel from siphoning when the engine is off or at idle. However, one thing I do remember about both my 45's is they tended to "leak" fuel out of the carb when off if tank pressure wasn't released. Not sure why, both did it from day one and ran great. But you might check the regulator anyway if you are having problems... might have a bad diaphram or some gunk in there on the seat. None of my YS 4strokes leak when off, it was only the 45's. My sugegstion would be to always release tank pressure after a flight.

If you should need parts for the 45, try calling Central Hobbies. www.centralhobbies.com They have been my best source for YS parts. If they don't stock YS45 parts, they could probably point you in the right direction. You can also go direct to YS, at www.ysperformance.com