Hi Amanda,
You need fuel, compression, and spark for the engine to run. Some more information would be helpful. Did the ski run in the past and just recently have problems? How long since it last ran OK (has it been sitting)? Do you have fresh fuel in the tank?
Things to check: Do you have spark at the plugs? Is gas reaching the carb (check the fuel filter........easy to get clogged. If it has been sitting with gas in it, the carb may be gummed up and need to be cleaned and rebuilt...........very common problem on the older 2 stroke skis)? Is gas reaching the cylinders from the carb? You might try putting a little premix fuel in the spark plug holes replacing the plugs and seeing if it will start for a few seconds, then you know it is a carb problem. Is the engine actually turning over. Watch the impeller when someone hits the starter to see if it turns. If not, pull out the spark plugs and see if you can turn the impeller by hand. If this ski was run in salt water, then not run for a while it is common for some rust to lock the pump system up keeping it from being able to turn.
If you have verified that you have spark and fuel to the cylinders, and the engine is turning over, but still not starting the next step would be to check the compression of each cylinder with a compression gauge.
As you can see there are lots of possibilities. Hope this gets you started.
