I flew mine for ever without a cowl,it didn't look awful,but was definitely better with it.Hilleja,I had an Os .91 FS in mine,inverted,it worked fine.I removed the cowl because inverted makes the carb way lower than the fuel tank and it gravity feeds fuel to the carb when it is sitting and causes hydralock.I broke a valve spring when it kicked back due to a flooded condition.I removed the cowl so I could put a pair of hemostats on the fuel line when it sits between flights.Also be careful,if you try to turn it over with fuel in the carb,guess where the fuel goes!!Not in the engine,thats for sure.BTW the cg in the book is way conservative,It will eaisly fly at 6 to 61/2 inches back,with no bad tendicies.
Mike