I have a 1990 js550 that i picked up for a project. When in the water it overheats and minimal water comes out the tell tail. When on the tap it runs fine no overheating, so i disconnected the hose from the back of the ski where it sucks the water in and ran a garden hose directly to it. And the ski ran fine.I also cleaned all the tubes out with air.I am not getting enough water flow through the ski when it is in the water. Is there a water pump inside the motor?There is definitely no blockages, there is just no enough pressure to keep it cool.Thanks
Hey Sam, It's Jeff again. I used to own a stand-up ski a while back, and I had the same problem. The water to the motor comes from the jet pump, the more RPM, the more pressure, There should be enough pressure to keep the motor cool at low RPM, but if not then there are a couple of things to check. Since you already eliminated a blockage in the motor buy disconnecting the pickup, first check the actual pickup for a restriction from the entrance to the connection you took the hose off at. If that's OK, then the clearance in the jet pump itself could be excessive. A ski with a lot of hours in sandy water can have pump wear that isn't really noticeable when cruising, you might notice it a little under heavy acceleration when leaving the no wake zone. Under idle there just isn't enough pressure to cool the motor. You can have it fixed for not to much, a little hard to do yourself. To save a planned day on the lake you can always get a cheep inline electric water pump. My last thought though, since your other question was about a slow cranking starter, I'd pull the plugs and spin it over to see if it spits water out the cylinders. It doesn't hurt just to eliminate a blown head gasket. As a side note, I like them a lot better then the big sit-down style, they're much more free then the bigger ones. It's like the difference between a motorcycle and a car. If you want to do the stuff the bigger ones do, buy a boat.
