Just to clear things up, I under stand that the engine ran good in all attitudes, then started dying when flying inverted, then started dying during any type of flight.
Was there a time laps between flying good and dying during inverted flight, like say a winter non flying season, or did this just happen overnight, as in Saturday it flew inverted without problems and then the next Saturday it died during inverted flight.
My first guess would be a pinhole in the fuel line inside the tank. Some of my planes however, after sitting through the winter, sometimes get "floatys" in the fuel tank, which are little chunks of debris from the oils used. The floatys don't seem to re-dissolve in the fuel when you start flying again, they just float around and clog the needle valve intermittently. These floatys do not have to be very big to give really strange results with the running of an engine.
Another theory that just came to me is perhaps your exhaust pressure line is being clogged somewhere. Maybe the muffler nipple. Perhaps the little extra pressure of the fuel on top of the exhaust vent while inverted was enough to loose muffler pressure, and then the blockage got worse and eventually the tank was not getting any pressure at all. I could see that depending on how the plane was stored (if stored) through the winter, some debris could have plugged up the exhaust line a little bit.
A hole in the exhaust pressure line could also cause the same problem. The hole could stay somewhat closed with low pressure and then open up when under higher pressure.
Last edited by flybyjohn; 03-11-2015 at 05:46 AM.