Thanks for all your thoughts. It was just enough to get my brain in gear, build a run jig I could mount the .61 in and play with orientation. I can offer my experience...for what it's worth. Oh, the engine was already well broken in. I flew it right side up in another plane for all last season.

Got the thing mount right side up tank set with feeds mid carb. Started it up, warmed it up and tuned it just slightly on the rich side. Made sure it responded nicely to hard throttle ups off idle and that it idled well.

I then shut it down, flipped it 90 degrees and ran it again. It ran just as well as right side up. Same kind of quick response from idle and it idled well.

Now for the test. Mounted the jig upside down and started it up again. It responded pretty much the same as the other two runs, with one minor exception. If it let it low idle for a half minute or so and then went to full throttle it would hesitate a bit. Twice it stalled. As long as I went easy on the throttle from idle it ran fine. I guessing there may be something to the plug fowling theory.

Anyway, not enough trouble for me to worry. The cowling is going to look great without a big gaping hole in the side of it. Thanks for all your comments.