Failed first engine start

Bob, 

The injectors seem like the most probable cause.  The way the coils are arranged, you would need to loose all four ignition coils to fail both the top and bottom plugs of cylinders 2 and 4. While it’s true that you would need both injectors clogged to have a totally cold cylinder, I think that is more likely.  You may also have one of the injectors clogged on cylinders 1 and 3 and they are limping along on one injector.  There are injector cleaning services, but Rotax would say replace them all. Maybe you could have them cleaned as a test, and if that solves the problem you could then decide to replace them. At least it’s a lot cheaper test than replacing them and having that not be the problem.