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Yamaha carb'd 4 cylinder auto shut down when overheat

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  • Yamaha carb'd 4 cylinder auto shut down when overheat

    I just finished putting one of these motors in a polaris rzr side by side. Upon riding and testing I encountered an overheat light and the motor completely shut down while accelerating. It did this several times and I wanted to share my findings on here.

    The sleds are designed to shut down automatically if sled overheats and there is no throttle movement for "x" amount of minutes. The sleds have a switch built into the throttle block. When on the throttle, the switch has continuity. Since the switch is a normally open switch, the motor runs perfectly fine with it not hooked up. While running, the ECU thinks there is no throttle movement and therefore when the overheat light comes on it is shutting down the motor.

    I wanted to share as the logic of this shut down feature could very well be overlooked by those using these engines. I plan to do some investigating on other models as well to see if the logic is the same.
    717-821-9639 call or text

  • #2
    Thanks so much for sharing this info, Tim. There are still mysterious modes of the ECU that need to be identified.



    • #3
      Thats weird because Ive been running my latest install without the coolant temp sensor connected. Because there was no affect i figured the sensor was for the dummy light in the display and to turn off the carb heaters after the engine reaches a certain coolant temp.


      • #4
        The switch you describe on the throttle sounds like the TPS (Throttle position sensor) The only thing I have heard it is used for is to compare the position of the throttle at the engine with the position (open/closed) of the throttle at the handle bar. Snowmobiles have trouble with things freezing and if the hand lever is not depressed and the engine is not at idle RPM, it will shut the engine down. For the temp sensor on the engine I converted I looked in the manual of how to test the switch and what its nominal values are. For example usually temp sensors are a certain value of resistance which changes as they heat up. The manual said something like the value should be X ohms when cold and Y ohms under normal running temps. I replaced the sensor with a resister that matched the Y value (so the engine always thinks it is up to running temp) and then put a 3rd party probe in the hole on the engine and ran that to a gauge in the cockpit. The engine I converted was a carbed 3 cylinder.