Just ran across this topic. I have a 90FX inverted in a SuperSportsSenior (World Models) that has been nothing but a major pain when it comes to getting that engine to idle decent. No matter what I do that engine will not idle for very long before it gets snuffed out. I just got a plug with a idle bar and will try that out. I also lowered the fuel tank so it is slightly lower than the carb. Do these regulating pumps really make the difference between success and failure with the inverted engines? I love the plane but this inverted engine is causing me much stress.