I have followed this thread hoping for someone with the same problem as mine to show up. I have had the same type of problem with a 3W 150 in a Carden 330, when inverted it runs rich, the attitude is exactly the same as upright so there appears to be no included airflow condition. Here's the kicker, it will run blubbering forever, I am talking minutes here, it doesn't die and as soon as I role back upright it clears up. I am having a hard time believing it is a carb block leaking. The needles are set at 3/4 and 1 1/2 any lower on the low and it won't start. I do have the carb vented to the fuselage with a short line, 6 inches or so.

Does anybody have any suggestions.

Chris