My 2011 yz450f

10 replies to this topic
  • Bradford690

Posted August 16, 2014 - 05:02 PM


My 2011yz450f is really hard to start.. Any ideas

  • bigcozzybear

Posted August 16, 2014 - 05:58 PM


You're not twisting the throttle when you kick it are you?
Mine fires on the first kick every time

  • dirtbeater

Posted August 16, 2014 - 07:32 PM


No fuel. That is the first place I would start

  • ratom98

Posted August 16, 2014 - 11:37 PM


check your valve clearance

  • Bradford690

Posted August 17, 2014 - 10:49 AM


No fuel. That is the first place I would start

what do u mean by no fuel? Fuel in the lines?

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  • dirtbeater

Posted August 17, 2014 - 11:11 AM


I would wonder about fuel pump and filters. I have never messed with an FI bike though. I just stick to the basics first, fuel, air, compression and spark.

  • xSX450

Posted August 19, 2014 - 10:52 AM


pump it a few times quickly to get the stator going, then give it a hard one. Also mine always starts much easier with 1/4 throttle... now with the gytr piston and cams its another story :(

  • Milliken721

Posted August 19, 2014 - 07:29 PM


On my 11' I get on it, pull the starter/idle knob out, and kick it twice very slowly. Then I kick it slowly until I find the sweet spot with the most resistance (TDC) and kick it hard and hold it at the bottom of the arc. It starts 9 times out of 10. If not, I just find TDC again and it always starts second kick. When hot, same thing minus pulling the knob out. If thats not working for you, try turning your idle up a click or two on that knob (clockwise if I remember right) and that should help. If all else fails, like someone else mentioned, check your valve clearances. My bike was getting harder and harder to start this summer and the cause was two tight intake valves. Hope that helps!

  • grayracer513

Posted August 20, 2014 - 06:51 AM


Then I kick it slowly until I find the sweet spot with the most resistance (TDC)


So we're clear on it, that IS NOT TDC.  The "hard spot" is the point where the exhaust valve is allowed to close by the auto decompression system and the COMPRESSION stroke begins.  That takes place roughly 25 degrees BEFORE TDC.  In an engine without auto decomp, compression at cranking speeds begins as soon as the intake closes, about 120 degrees before TDC. 


TDC is "Top Dead Center", where the piston is all the way up as far as it will go.  You can feel it go past TDC by pushing against compression until you feel the engine pop forward to a second hard spot.  That's where it rolls over the top and you're trying to force it down the bore against a vacuum with all the valves closed. On the compression stroke, TDC happens after the spark, so if you kicked it from there, the engine would have to make two full turns before it had a chance to fire.

  • Milliken721

Posted August 21, 2014 - 09:21 PM


So..... Yeah, kickstart it.. 25 degrees before TDC then. I shouldn't have thrown out TDC, I just know where the sweet spot is on my bike by feeling, I said TDC because the last magazine review on the 10'-11' 450's mentioned it being impossible to start unless you find TDC first. I assumed that since my bike starts first/second kick every time at my sweet spot it must be TDC, bad assumption apparently /:


Thanks for schooling me up!

  • grayracer513

Posted August 22, 2014 - 07:06 AM


It's an extremely common and deeply ingrained misnomer to call "the hard spot" TDC.  Probably most guys do that, but it's nevertheless incorrect, and causes confusion. 

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