RE: You Can Do Engine Problems
In my experience (aside from whatever starting issues that may go with an inverted engine), tank location r/e the carb DOES make a difference. I own a U-Can-Do .46, with an OS 70 - mounted sideways, not inverted. This has been a great combination - with a very trouble free running engine. It was used when I purchased it.
Of the points raised before: yes - a non-broken-in engine can be troublesome, at first. Some of the Chinese engines tend to have harder cylinders and / or rings, and take a longer time to break in (vs. an OS, for instance).
As to the tank location: in the short term, it doesn't matter - i.e. you can fly your airplane upside down, climb vertically, etc., it'll still run. BUT - over a 7 - 10 minute run, tank location does. Try holding your airplane running nose down, idling, for several minutes. You will notice a difference.