ORIGINAL: TimC
Yes low@slow, from what I've learned here at RCU, an air-bleed carb can be a bear when the engine is inverted. I've never tried it though. rctrax, that is a very good tip about grinding a servo wheel into an eccentric to operate a micro-switch. How did you grind it?
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You don't need no esteenking onboard glow for normal engine operation. You do need to ensure that your fuel tank centerline is not too high when compared to the spray bar centerline. You also need to drop your membership in the "1/2 turn only low speed adjustment club". <G>
Visit a pattern contest. Note all of the inverted four-stroke engines being used. Ask the pilots if they are using onboard glow heat. They will probably begin laughing as though you told a hilarious joke. Now, after you have discovered that adjusting a four-stroke engine for good inverted running is, indeed, possible, go home and get some practice adjusting your engine. Adjust it until it runs right. Don't be afraid to try different glow plugs, fuel, etc. In the end, the fuel will probably end up being YS 20/20 or something close. The glow plug will end up being an OS Type-F, or a clone of said plug.
There is nothing wrong with the OS FL-70. There is nothing wrong with an airbleed carb. If there was, YS would not have used one on their early YS-91 and Enya still wouldn't be using them on some of their high performance engines.
Although the FL-70 is ringless, I imagine it will take a little running time until the engine stabilizes enough for fine low speed carb adjustments to make much of a difference. You don't take a brand new engine out of the box, pop it onto a model inverted and then expect it to run perfectly immediately. For the low price of our engines, it is a miracle that they run as well as they do.
Try as hard as we might, these days, one must spend some time with their glow engine and their running characteristics in order to run them successfully. These are technical little beasts and they require the owner/operator to familiarize themselves with their running characteristics. If you don't have time to do this with a glow engine, do yourself a favor and go electric. There simply isn't any way of eliminating wrapping your noggin' around one of these fine little creatures in order to extract maximum performance.