Yup, inverted engines run just fine... I have an inverted 2 stroke and inverted 4 stroke.. No problems... There are however two things to keep in mind... Tank placement is important... If your tank is too high above your carb (as it can sometimes be with the engine flipped over) you will get fuel dripping out of the carb with a full tank of fuel and the engine not running.... Second thing to watch out for is it's MUCH easier to fluid-lock the engine when it's inverted... EVERY time you get ready to start the engine (Assuming your using an electric starter) ALWAYS turn it over a few times by hand to make sure it flips okay... Otherwise if fluid builds up in the head it will lock the piston (fluid doesn't compress like air) and with a strong electric starter on it it's not hard to destroy your connecting rod.