I just had a heck of a time trying to get my Magnum .91 FS to idle inverted in Nitromodel's 90 sized Extra. The engine ran great right side up, but wouldn't do it inverted. I was getting so mad, I almost gave up, but a guy at the LHS told me to check the valve clearances (btw this is my first FS). I did that today, and the valves were about 3 times as big as they should be on the larger side. Keep in mind this engine was brand new, and just got 1 gallon run through on a test stand, and it ran great. Anyways, after I fixed the vlaves, I set the low speed and high speed needles, and the engine no only idles like a dream very consistently, with ne chance of it dying, but it has more power now too! So my answer to running a FS inverted is that if you have it tuned and set up right, and you take care of it, you will have no problems whatsoever. Just break the thing in rightside up on a test stand so you can run it rich enough.

Scott