ok today i went riding and was back in the woods going slow and steam started blowing out of the radiator overflow. checked the coolant level after it cooled down and it was low so i filled it up rode about five minutes then checked itand toped it off. went riding deep in the woods again about 30 minutes and did it again. anyone have any ideas? i just bought the bike so im still learning about it. could it be carb running lean does anyone know the stock jets and settings so i could check that. any other ideas would be greatly appreciated.

It just sounds like you are riding too slow. If you are not getting air to pass through the radiator than it can't work effectively. Try putting a few capfuls of Red Line water wetter. That should bring the temp down a few degrees.

it is also a 1998 yz400, stock pipe and every thing except a flywheel weight. thanks for the help

My 98 YZ-400 used to overheat out here on the desert trails. I found a few things that helped. I replaced the o-rings on the metal tubes that connect the radiator hoses to the engine. They leaked, but it was hardly noticeable (water was down after every ride even if it did not spit from the cap). I started using red line water wetter, and got a higher-pressure 1.6 radiator cap (KX-60 or 500 I believe). It still pukes on really long slow up hills, but is mucho better now. Also, pull the water pump housing and check for debris, you may find some sludge in there.

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