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Ask Kenny O. Your Own Question
Kenny O.
Kenny O., Personal Watercraft Specialist, Kawasaki Jet Ski, Yamaha Wave Runners, Sea Doo Watercraft
Category: Boat
Satisfied Customers: 953
Experience:  Product Specialist Kawasaki Factory Support 24 Years, 8 years National Technical Director IJSBA
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I have a 1989 Kawasaki JS650 X2 that runs great

Customer Question

Hi, I have a 1989 Kawasaki JS650 X2 that runs great for several minutes then starts overheating. The water bypass flows water normally at first then as the engine warms up there is less and less water flowing out of the bypass. Also the exhaust gets louder and louder as there is less water in the exhaust as it heats up. When I shut it down I can hear water boiling. I replaced the head gasket thinking that was the problem. No change in symptom. What else could it be? The engine runs strong and good except for getting hot. Don't want to damage the motor so I shut it down...
Submitted: 1 year ago.
Category: Boat
Customer: replied 1 year ago.
The rubber cooling hoses do not appear to be soft or collapsing when hot. I pulled the exhaust manifold looking for sand or other deposits in water passages but it was perfectly clean. Reinstalled exhaust with new gasket and no change in symptoms.I have never replaced the bottom end cylinder gasket I don't think I have ever opened the water drain valve under the crankcase nor have I split the case to replace those gaskets. Could an air leak cause my symptoms?
Expert:  Kenny O. replied 1 year ago.
Hi thanks for the request, it definitely sounds like a water flow problem except when its gets hot, its sounds like you have done your do diligence and have eliminated the exhaust for any obstructions, and an exhaust hose that might be de-laminating on the inside can cause excessive heat in the engine but will usually come with a runnability issues. As the engine gets up to operating temperatures its demand for a good water flo is going to be more critical, I'm sure you have check for obstructions from the pump forward but make sure where the cooling line attaches to the exhaust manifold is not doing anything funny when the hose gets hot, there is alot of heat on those fittings. The only other thing i have see on these if the timing is doing something funny which can throw a lot of heat into the engine, Has anything been check in the ignition ? Also to rule out a cooling issue say in the line, is get a long hose and run it direct from the fitting on the pump, run the hose on the outside of the ski directly to the fitting on the manifold, this will eliminate a line that might have colasped where it runs through the hull, let me know if this helps or you have more questions, we can continue on ! ThanksKenny
Customer: replied 1 year ago.
I don't think there are any obstructions since the water flow starts out strong and becomes less as the engine warms up. Does this engine have a thermostat somewhere that regulates water flow?Ignition timing is factory stock. Never modified. Has a "West Coast" exhaust and factory water box installed. Could improper cooling hose routing or connection cause the problem?Could a bottom end leak send air through the cooling system when warm, pushing back the flow of cooling water? Lots of "air" and exhaust sound is exiting out of the water bypass when hot. makes it seem like an air or exhaust leak is a possibility, but I don't want to pull the engine out of the hull unless this will definitely solve the problem.
Expert:  Kenny O. replied 1 year ago.
I agree the flow is enough for when the engine is not up to its normal temperature and is likely not the issue. There is no thermostat and its critical that the water flow is correct, also if you are exiting too much water that can have an effect also, i think you need to pull the pipe and inspect it on the inside, those are water jacketed pipes and maybe when its heating up its opening up and water to by-pass where it shouldn't be ? I dont think you have an air leak because you haven't said that the ski runs bad, this has a simple water flow, you bring water in the exhaust manifold and then the water gets pushed up through the cylinder, through the head and then out the front of the head to feed the exhaust, again if you are exiting too much water and or not enough to slow the flow down then you can get an over heat situation, I think you have a timing problem, maybe the flywheel key shured ? Kenny
Customer: replied 1 year ago.
Okay, thanks for your help Kenny. I will pull all the cooling lines and replace them (in case they're delamination inside when warm).I also might add a second cooling line up from the jet pump. The head has been shaved and has higher compression than normal. This could be contributing to a higher heat load for the factory cooling system to carry... I don't know... Just want to ride!It ran fine for years after the engine and exhaust pipe mods were performed in 1992 though... UGH! The overheating began in 2001 and I cleaned all the lines then. Problem wasn't fixed. the ski has been sitting in storage since then since I couldn't figure it out and got frustrated. I assumed it was a blown head gasket related to the high compression.Found some time recently and decided to replace the head gasket. The engine fired right up after disassembling the carb, new gas, and battery and I believed I had solved the problem after backing the trailer into the river and idling the motor in the water for a while. Great flow out of the bypass outlet.Decided to unload and ride and it didn't take long at full throttle to realize the problem was still there. Very sad and disappointing.You have convinced me not to tear the engine apart and replace the gaskets. Thanks for that! At some point I may put a block off plate on the crankcase water drain since many online complain about them leaking crankcase pressure once the o rings on the drain valve crack.I'll focus on the cooling lines. I believe the cooling water pipe coming forward from the jet pump is a hard line, maybe metal or hard plastic. It is encased within the fiberglass hull and can't be replaced. Maybe I'll reem it out to be certain it's clear of debris...I will pull all rubber cooling lines and plastic fittings and will replace them.I will pull the exhaust pipe and exhaust manifold and make sure I didn't install the cylinder to manifold or the manifold to pipe gasket backwards.I did pull the exhaust system apart before the problems started. Maybe the new gaskets / orientation have some cooling passages blocked.I will keep at it until the problem is solved! Thanks for your help though!
Expert:  Kenny O. replied 1 year ago.
OK sounds Great, let me know, loved these old skis !
Kenny
Customer: replied 1 year ago.
Kenny
I would like to thank you for your help. The jet ski is not here with me. I left it at the lake. The next time I am there I I will replace all the hoses and will pull the exhaust gaskets off to be certain they're installed correctly and aren't impeding the water flow.You have been a great help though as you have talked me out of thinking it is a bottom end air leak that was causing the water flow problem.The more I think about it the more I believe that the water flow at partial throttle is sufficient but at full throttle the engine is boiling off an insufficient water flow caused by a partial blockage in a hose or maybe an insufficient sized fitting I may have installed some years ago. I'll check everything in a few weeks when I'm able to get back to the lake.Do you need me to click a rating or something evaluating our interactions? If so, where can I access the link?Sincere thanks for your help!Richard WadeLove the 2 stroke smoke!
Expert:  Kenny O. replied 1 year ago.
LOL Awesome picture !
Thanks
Kenny

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