Hi Lee,

I'd like to add two other answers to your original question. First, in my own opinion and experiences, gas engines are less sensitive to mounting orientation than glow engines. For example, if a gas engine is mounted inverted in a war bird, I have found that the inverted mounting does not cause any issues with respect to how the engine runs or is tuned. I get the same nice, slow reliable idle regardless of the mounting orientation. I have found that four stroke glow engines mounted inverted are more difficult to tune for a sustained low idle and sometimes I have had to use a glow driver to get a nice, slow, reliable idle. Second, I have found that gas engines don't change how rich or lean they are running from the beginning to an end of a flight. Most of my glow engines would run leaner at the end of the flight than at the beginning. Not a big deal generally, but on some warbirds this would increase the idle to a point that was higher than I preferred, so I found myslef puting in a few clicks of down throttle trim at the end of each flight. I don't have to do this with gas engines.

Good luck in whatever choice you make!

-Ed