426 running hot

i have a 2000 yz426 and it runs real hot after a min or so of riding or letting it warm up and the coolant will boil out the over flow and the level in the radiator will go down after a bit of riding i was told that the jetting might be a cause to it runnig hot just wonderin casue i dont want it to blow up again just had it rebiult this summer:confused:

I would say it's either jetting or maybe the water pump isn't working right. Check the water pump/impeller and see if it's ok. If everything checks out, try richening up the carb mixture a bit. You can pick up some main jets at a dealer pretty cheap. Also check the air/fuel screw and maybe shim the needle or drop the clip on it one position.

ok ill try that thanks

Another possibility could be a clog/block in the radiator or cooling system.

I can pretty much assure you that it isn't jetting. Try to get access to a laser remote thermometer (the little "guns" you can point at something and read the temperature of the object). Remove the louvers in front of the radiators, set up a fan to blow air over them, and run the engine. Check that the radiator temperature is reasonably uniform across from one side to the other of each radiator, and that the temperature is hotter at the top than at the bottom by at least 30-40 degrees with a good draft of air going across. Cold areas indicate obstructed tubes, and and insufficient temperature drop top to bottom indicates poor cooling efficiency due to scale.

Have the system and the cap tested for it's ability to hold pressure.

Test the coolant. Weak, old coolant boils too easily.

If the 2000 426 has the original cap I would replace it. Follow the grayracer!

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