Properly set up, an inverted engine performs as well as any other mounting. Tank location and idle adjustments are more critical though. You do run the risk of fluid lock (excess fluid in the combustion chamber) due to over choking or bad fuel tank placement which could cause you to damage (usually bent or broken crank rod) if you try to use and electric starter with fluid lock. A side mount is often the easier to handle, will tolerate some slight missadjustment of needle valves and is easier to get proper tank placement relative to the carburator center line. Attaching the glow plug clip can also be a problem in inverted mounting unless you instal a remote connector.