Ok. I have managed to get my simi inverted 4 stroke to idle over a minute from about 20 seconds initially. I did this by further breaking in the engine, playing with the tuning, switching glow plugs, and switching to a fuel with a lower percentage of oil. So how do you get this thing to run reliably? The engine is a TT F91-S, the fuel is 15% Omega (was Wildcat), the plug is a Thunderbolt FS (was OS-F and Fox Miracle), and the plane is the GP Fokker Dr-1 Triplane.

I have to add here that I have tuned it to the max, I have done the pinch test as well as taching the idle. It idles best just rich of max lean, just as you would expect, transition is great with glow, and without glow before it bogs down which is about after about 20 seconds of idleing. If you run it up to max and shut the engine down immediately compression is better than average for a ringed engine. If you check after it quits after over a minute of idling it will have compression almost as well as an ABC engine, it takes about 3 minutes for it to lose enough compression to stay at TDC. Obviously the extra oil flowing down into the cylinder increases compression. Only adding this because some of you think that an inverted 4 stroke should act just like an upright one, but just as with a two stroke the extra oil flowing into the glow plug make some engines problematic.