One of the likely reasons for the engine not starting is lack of fuel so over the period of the starting trials we checked: -by disconnecting fuel hoses and turning on the electric fuel pump determined that fuel was getting to the mechanical fuel pump and also through it to the carburetors -that there was no water in the gasoline using the gascolator test valve -that there were no tight turns in the fuel hoses at the carburetors resulting in loosening the bolts and turning the banjo fittings to take out kinks in the hoses -that the Bowden cables to the throttle levers and to the starting carb levers were not restricted and the curves were not too tight
Finally as stressed in the Rotax manual and the available videos I verified that the carb idle speed screws were at the correct setting (1.5 turns in) and also the idle mixture screws (1.5 turns). Some fooling around with the throttle cable fitting nuts at the carbs got both cables to move at the same time as best as I could (this is called the mechanical synchronization, with the pneumatic synchronization to come later).
