kawasaki550

This summer I bought an 87 JS550 that is mechanically bone stock besides the previous owner bypassed the stock fuel filter and put in a normal fuel filter in it. It will run great for about 30-45 min of consistant riding, after that if I fall or just stop and let it idle it will die after about 1-2 min of idling, it will run after it dies but only at full throttle and it only goes idle speed. I have basic knowledge of jet skis seeing this is my first ski and looking for any ideas on what could be going wrong. Any help greatly appreciated!

KHB

Well here are at least a couple of ideas. One possible problem could be vapor lock. The engine compartment could become warm enough the gas is on the edge of going from liquid to a vapor state. This is not that uncommon, my fuel injected ski boat will experience the same symptoms when under heavy load on a hot day. To solve that I run the blower on hot days, problem gone. Additionally it would not hurt to inspect the fuel system and replace filters. I would even go as far as dis-assembling the carb to inspect and clean it. Those steps are probably not needed but at least you will know the condition of the supply side.
Back to the possible vapor lock issue, does the engine have enough fresh air intake to keep a good supply of fresh air avaliable? I suspect if you let the engine rest/cool for a few minutes the problem is gone. Checking the coolant system to ensure proper cooling is also in order, as that would increase the temp in the engine bay.

Good luck I suspect the solution is an easy one.

kawasaki550

I kinda thought it was vapor lock this summer so I changed the fuel filter they put on there and I insulated the fuel lines the best I could and it helped a little bit but not solving the issue, would it help if I replaced all the fuel lines? or maybe the carb isn't pumping enough fuel in? It should have enough air getting into the engine because there is a big scoop on the hood for air and the cooling system seems to be working, it's shooting water out of the exhaust just fine.

KHB

Replacing the fuel lines would do nothing I suspect. As for fuel starvation you would see the effects of that while it was running towards WOT. Another thing to check as you mentioned is the fuel pump. I have seen situations where you can have positive case pressure that can pump fluids through the pumps pulse line. The end result is a fuel pump that becomes hydraulically locked. Once the engine stops pressure and fluid leave the pump and it will run until that happens again. Sadly high crank pressure is usually associated with an internal problem. Many times it a bad head gasket or piston rings that are allowing blow by. One way to check is to remove the pulse line from the fuel pump and if it has gas and oil in it odds are that is your problem. Some fuel pumps will have a vent screen which has and oil may be coming out of, again that is bad. If you see evidance in the pulse line or pump vent I would do a compression test and a leak down test to see which cylinder seems to be the problem. Fuel issues can be tricky because there can be some dynamic things going on that you never think about. Good luck let me know what you find.

kawasaki550

I took a look at the pulse line and luckly it is a clear line and I can see that it has fuel and oil in it, so does that mean the piston rings are bad and I'm getting blowby?

kawasaki550

I did a compression test when I first bought the ski and both cylinders were at 120 psi