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  1. #1

    Where is the Thermo Switch located? '91 WR500p

    Okay so I picked up a couple skis for incredibly cheap, $400 for both from a friend that needed to sell, one is an 89 waverunner 500, and the other is a 91 waverunner 500.
    They were both recently rebuilt from the ground up, carbs cleaned, new hoses, new plugs, wires, exhaust tubing etc etc.
    Virtually everything is in perfect condition for the year.
    The 89 runs like new off the show room floor, but the 91 not so much.

    It appears to be stuck in the dreaded "limp mode".
    I have swapped the carbs from units to check if that was the issue.
    Checked the impeller clearance, it looks almost brand new with no dings in the three blades at all.
    Checked all hoses/exhaust for blockages, all port and drain holes, everything is clean.
    There are no exhaust leaks at all.
    Perfect compression on the cylinders at 150.
    Starts right up, no choke required, idles fine, squirts water on hose and in water just fine. Water temp from the the rear seems normal and the same as the 89.
    Everything is in perfect running condition.
    The motor runs very cool so I know it is not over-heating and from researching here it seems to point to a bad thermo switch.
    My problem is I have no idea what it looks like/where it is located.
    I've looked EVERYWHERE at every dealer here in San Diego for a freaking manual and nobody has one.
    I ordered one from South Bay Motorsports, but its going to take more than 2 weeks to get here....
    I really wanted to have both ski's up and running to surprise my girlfriend when she gets back from her trip to Michigan next Thursday....

    I want to disconnect the switch temporarily to make sure that is what is putting this ski into limp mode.
    The only thing that I can see with a wire heading into the head of the motor is this, but it looks a little large and don't want to try disconnecting and messing it up any worse....If anyone that's worked on these old waverunners before can shed some light if this is the thermo switch or can take a picture of its location, you would instantly become my hero.

    Is this it????
    Ignore the water on the head, it was raining pretty hard when I was trying to snap a pic.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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  2. #2
    Also, if that is it, could I cut/disable it to test the ski until I get a replacement?

  3. #3
    Seriously?......39 Thread views and not one reply?

  4. #4

    Join Date
    Dec 2012
    Corpus Christi, Texas
    That look likes a themo to me. My 97' 760 has the same type of thermo - just in a different location. I'm not sure about the disabling part of your post. Give it a couple of days. Someone on this site knows your 91' 500 inside and out will come up with a good answer for you.

  5. #5
    SkiSwede's Avatar
    Join Date
    Apr 2009
    Denver, NC
    That is indeed the thermoswitch, and your symptoms are dead on. Open the ebox and simply disconnect it.

  6. #6
    Nickeljet's Avatar
    Join Date
    Feb 2007
    Moss Bluff Louisiana
    You can replace the CDI with one from the same year 25 Yamaha outboard but it does away with the rev limiter and heat sensor. The original cdi is almost impossible to find but if it is not the sensor this is one way to solve the problem.

  7. #7
    Quote Originally Posted by Nickeljet View Post
    You can replace the CDI with one from the same year 25 Yamaha outboard but it does away with the rev limiter and heat sensor. The original cdi is almost impossible to find but if it is not the sensor this is one way to solve the problem.
    Kinda unable to find either, and at this point, I'm honestly to the point that I don't care to fix this ski.
    Everyone that works on them here in San Diego wants an arm and a leg to even take a look at it and diagnose it.
    And all state that the parts are going to end up costing a ton, and take forever to source.

    Seems more useful as scrap.

  8. #8
    Just to update, I took it out of play and disconnected it and it still won't rev and remains in limp mode.

  9. #9
    i have the clymer yamaha water vehicles shop manual, 1987-1992. and i didn't fine anything about a temp safety but i could be wrong. the only thing i saw in the book i can think maybe could give you trouble is is the thermostat greased? if they were rebuilt from bottom up maybe they forgot to do that on this one and the vibration is making it think its overheating? i'm not too good with electrical stuff but i've seen stuff online about the older waverunners doing this although we have not had this problem. knock on wood.

  10. #10
    kinda like this? it wasn't the exact video i was searching for but its close.

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