Jet-ski troubleshooting can be broken down into a few groups. If the ski will not start or run at all, the ignition should be the first place to start. The carburetion or fuel system could also cause this problem if it hasn’t run in awhile. A spark plug check is a good place to start for either problem. Remove the spark plugs and look at them to see if they are wet or dry. If they are dry and light brown color the fueling is correct. If one plug is wet, either that carb has a problem or the ignition on that cylinder isn’t working. Use the starter and spin the engine over with the spark plugs in the plug boots. Lay the plugs on a unpainted metal part of the engine. As the engine spins the plug should be sparking. If the spark looks weak or both plugs are wet and black the plugs may need to be replaced. NGK spark plugs should be used because they work very well for two stroke engines. If one spark plug isn’t sparking the ignition coil may be bad. Refer to the ignition coil story to learn how to check a coil. If both plugs are good but are still wet you may have a carburetion problem.
Decide if the problem occurred above or below approximately 3000 rpm’s or occurs always. Below 3000 rpm is the idle circuit which is controlled by the low speed jet. Above 3000 rpm’s will be the main jet. Remove the jets and hold them up in the light to verify that you can see through them. In diaphragm carbs the pop off pressure, is also very important to low speed and acceleration. This is controlled by the spring that offsets the diaphragm pressure used to allow the feeding needle to let gas in. If one spring gets weak that cylinder will become rich randomly. If the infeed needle is stuck the carb will get no gas. If both carbs are getting no gas, remove the fuel pump line and spin the engine over. There should be gas spraying out of the lines as the engine spins. If the pump doesn’t seem to be working, check the center line (vacuum) to the pump, and look for leaks. Also verify that you don’t have an exhaust leak in the engine compartment. Partially remove and slide the seat back 4 inches to keep fresh air in the compartment. If the air is contaminated with exhaust the jet ski will run o.k. initially and get worse the longer it runs.