YZ400F overheating,

3 replies to this topic
  • strasstn

Posted June 09, 2005 - 09:26 PM


Hey Gents,
K, I've spent the last 5 weeks cursing dirt-bikes. Die-hard sledder here, bought my first bike (YZ400F), and have messed around for 5 weeks trying to get it to run.
Long story short, after completely breaking it down, metal was in the cylinder! Carb's been cleaned and set to factory. It WAS running ruff, but popping like crazy all the time, not just on deceleration.
Now, luckily, it runs great (Lord only knows how I managed to rebuild an engine my first time but hey, :) ).
But, problem is, it overheats as soon as I am not riding it. I've read some posts that say it's a common problem, but c'mon, there's got to be a solution. Is is just running too lean at idle to 1/4 throttle?

Help me out. I mean, even my new Mach Z 1000 twin SDI runs all day everyday, first pull, never runs hot, just add gas and oil, and 6000 kms later, no problems. Are bikes really this tough, or am I missing something?


  • kizzle426

Posted June 09, 2005 - 11:10 PM


Point in case is YZF's do NOT like to go slow. There are some things you can do to help. Boyesen makes a supercooler water pump cover that helps out big time. That should help stop the anti-freeze from spraying all over you. About the popping, you can move the clip on the needle in the carb down one notch from stock position and get a larger main jet if necessary. I had to move the clip UP a position and get a smaller main jet on my 426. There are some other things you can do to help the over heating situation but the supercooler should do it. One thing is for sure, don't let the bike sit there and run for to long without riding it....that's a definite over heat situation. Anyway....my 2 cents.

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  • Butta

Posted June 10, 2005 - 05:59 AM


I'll throw in the idea to check the condition of the radiator cap, as well. I like to start with the simple fixes first.....

I've run my 400's and 450 slow at times in the Florida heat and have never lost coolant....maybe I'm just lucky? but I've kept an eye on it and I don't let them idle sitting still.

  • Frostbite

Posted June 10, 2005 - 01:50 PM


Hey Gents,

Help me out. I mean, even my new Mach Z 1000 twin SDI runs all day everyday, first pull, never runs hot, just add gas and oil, and 6000 kms later, no problems. Are bikes really this tough, or am I missing something?


Your bike needs air moving through the rads just like your sled needs snow spraying up on the heat exchanger. The coolant in your sled flows all the way down the tunnel to the exchanger and back, so it gets more of a chance to cool. The bike rads are sitting right beside a hot engine and exhaust pipe. When you're moving the heat is blowing away from the rads but going slow or sitting still the rads actually pick up heat radiated from the engine.
There are a few things that make the overheating worse, a weak rad cap like Butta said or a lean mixture. Check your right rad. I bent mine slightly in a crash and it moved in closer to the pipe. Heat from the pipe was boiling the coolant in the bottom tank of the rad. Bending it back out cured the problem. I also stick a bit of reflective tape on the bottom of the rad to reflect pipe heat away. A new or higher pressure rad cap will increase the boiling point of the coolant so although it gets just as hot, it won't boil over.

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