I don't know anything about jet skis, but after trying to start it, are the spark plugs wet with gas. If so, it's not firing. When you took the carburetor off, did it have gas in it? I've watched a few videos on start up procedures and those guys turn on the gas, pull and hold the choke out and they just turn the key for about a full minute before the things crank up. You need to make sure the plugs are getting gas and getting fire. You can spray some starting fluid into the breather snorkel and see if it starts with starter fluid. If it does you have a fuel delivery problem, if it doesn't you have an ignition (firing) problem.