First I will start with the question everyone asks is how do I know if I have sucked something up my jet pump ? Your ski will loose majority of power and vibrate like crazy when you try give it power, this is the water cavitating in the jet pump and is a sign that there is a good chance you have just sucked something up, BUT keeping in mind that other issues with a jet ski can cause this too but first check your jet pump for debris before cutting the chase thinking your engine has just blown up.
Rigtheo, if you have sucked up debris up your jet pump, I dear say you have done yourself a mischief. Some cases you may be able to fix it whilst out on the water and some cases you may have to be towed back, all pending on what has been sucked up and the severity of it.
Common debris/items people suck up. First is a ski rope, often I have seen people suck up a ski rope as they forget to keep an eye on it and slowly idle over the rope. Remember your jet pump is like a “vacuum cleaner” under your jet ski, and when you are in neutral your prop is still spinning and sucking water up, it is just being redirected back at it self by the reverse bucket so yes the vacuum cleaner is still in full operation under your jet ski. If you do this you must turn off your jet ski straight away ! putting the ski into reverse will not undo your mishap.
In this case most the time you will have to tow the ski back to a boat ramp and put it on the trailer to be able to cut free the rope as it is one hell of a mission to do underwater (learnt this the hard way) To cut the rope free you have to go under your ski whilst on the trailer and put your hand up in the jet pump and start working away at cutting the rope off the impeller shaft with a half decent knife, took me about 10 minutes when my buddy had sucked it up once in the surf.
The second common way people suck up debris is riding in rivers/lakes after storms when there is a lot of debris washed in from land. Good portion of the time when this happens you can tow the ski to the shoreline and have a friend assist in tilting the ski onto its side and you can pull out debris from the pump with your hand or a knife.
Third most common way to suck up debris is by riding in shallow water where there are fields of weed, very common in lakes and shallow water ways. Best thing to do if you all of a sudden notice you are in shallow water is to maintain speed to stay on the plain and keep riding with caution. The reason for this is when your ski comes off the plain it sits lower in the water by approximately 15cm or so and you loose the pressure between the hull and the sea bed. Again if you suck up weed there is a good chance you can remove it whilst out on your ride to avoid being towed back.
Now the fourth most common debris people suck up is rocks, these are a big no no as they damage your impeller and jet pump liner, this usually requires a rebuild down there. You will hear them rattle around so immediately turn off the jet ski and see if you can get them out.