If the engine gets flooded, it is a worse problem with the engine inverted than upright or side mount (exhaust down). The fuel will pool in the head and you can damage the engine if you force the prop to rotate. Also, oil or residue will lay in the glow plug well when the plane is stored with the engine inverted. This can cause plug glow problems when starting for the first time. A sustained low idle can be harder to get with an inverted engine although thats been my personal experience because I know of quite a few inverted engines that idle very good. I run a Top Flight (red box) P-51B Mustang in Shangra-La decor with a inverted ST 61 engine and I don't spend much time on the runway before take-off although it will maintain idle for taxing back.