YZ450F over heating

3 replies to this topic
  • Jtcaps05

Posted March 13, 2016 - 08:33 PM


Hey guys, I just got a 2007 YZ450F 2 weekends ago. I was going to change the oil today along with my yfz450 I got the weekend before. So I started the yz450f up and was letting it idle and warm up while I got the quad out to do the same thing. When I turned back around like a min later there was smoke pouring out by the radiator. I left it cool down. I changed the coolant out with new coolant and same thing happened. Now I heard it could be that 450's do this when they idle for more then a minute. I dunno if it true but that's why I heard. I don't know anything about this bike but I was thinking about it and does the fuel screw have any effect on it? I tighten it down bc he kept vibrating out but I don't think it should be tight. What about low on oil. The reserve says full but not much in the engine part. So I re filled the coolant did the whole tilt the bike to get the air out and then restarted it and let it sit for another minute or so and I turned around and smoke was shooting out everyone and out of the overflow tube. And now all he coolant is gone again but it didn't leak out anywhere on the floor. If anyone could help I would greatly appreciate it. Thanks

  • Krannie McKranface

Posted March 14, 2016 - 05:40 AM


Dude, you need to download the service manual, and read it!


No way to know exactly without seeing the bike, but more than likely, the radiator cap is bad, and should be replaced.

Yes, one the left radiator gets too hot to touch, you better start riding the bike or it will overheat.

One of the radiators has a 'bleed' hole to release air, plus you should run it with the cap off for 1 minute after changing fluid.


You NEVER add oil to a motor for no reason. You can blow a seal easily.

You cannot trust anything but meausuring the oil that goes into the motor. 

You should be changing the oil every 3 rides / 15 hours, and when you do, you should measure the quantity that comes out now and then, to see if you are burning oil.

You cannot trust the dipstick/site window/oil check oil for oil levels.


Your fuel screw is for idle only, and if yours is falling out, you have a missing oring, which would make it run very lean and overheat quickly.


Get an R&D fuel screw.

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  • grayracer513

Posted March 14, 2016 - 06:59 AM


First off, the oil thing.  It's a dry sump system, so there should be very little in the crankcase.  Read both these:






Regarding the overheating, you cannot generally expect a YZ450 to idle longer than 45-60 seconds at a standstill and be happy about it.  That's mostly normal, but if you don't stop doing that, you're going to do some damage one fine day.


The fuel screw is falling out for one or both of two reasons: it has no O-ring, or it has no spring.  The parts stack looks like the picture attached, form bottom to top, the screw, a spring, an O-ring, and a washer.  The baseline setting is all the way in 'til it bottoms, then back out 2 turns.  Then start the bike and warm it up before trimming the fuel screw out per the manual.


The Yamaha owner service manuals are available free here:





Attached Thumbnails

  • screw.png

  • Jtcaps05

Posted March 14, 2016 - 07:29 AM


So basically I just let it idle to long. Hopefully that's all. Thank you for your input

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