plugs could be fouled, could be full of ****ty fuel, so id be cleaning them/replaceing them and the fuel filter
If you have some ether or easy start spray stuff try spraying some into the air intake while some one cranks the engine over, you can also use a butane/propane blow torch (not lit of cause) to feed some gas in there, be careful doing this as it's very imflamable and may blow back from the intake.
If the engine fires and tries to run using this stuff you know you have a spark and the problem is fuel related.
Sorry if non of this makes sense, I'm a Pom. I just joined the forum as I also need some help with my Celsior so in return tried to help out with this problem