RE: Starting inverted engine?
I'm not an expert on pumped engines, but on regular glow engines, I usually don't have any problems.
The first question is: What adjustments have you made already? Can you go back to square 1 and start again?
The next question/suggestion was whether you ever had this tuned to run perfectly in the upright position before you mounted it, especially in the idle region.
These are just for starters. Just my $.02