2009 yz450f engine knocking!

6 replies to this topic
  • vic2340

Posted January 14, 2013 - 08:58 PM


I noticed the other day that my yz450f likes to knock some times and other times the engine stays quiet. Recently though it is knocking loud and wont stop. It has hesitation also on throttle response even though I have the jetting is set to stock and everything on the bike is stock. ( I bought the bike from someone however and see that the top end bolts have wear on them, I dont know what the top end could have in their) The knocking sounds exactly like pre ignition even though I am running 93 octane fuel. Has this happened to anyone else? The manual says to use 95 octane or higher ( I doubt anyone does that for a stock bike) anyways does anyone think that if I buy Sunoco 260 gt race fuel that the knocking will go away. I need help with this, my bike runs like hell. Also If I give the bike more than a quarter throttle fast the bike bogs hard and after high rpms it likes to pop.

  • FinchFan194

Posted January 14, 2013 - 09:30 PM


Out version of 92 is 95, someone else can explain it, but you are good with US Premium. Sounds like you have a dirty carb. My engine knocks and sounds like ass at idle too for the most part. These engines are noisy.

  • vic2340

Posted January 14, 2013 - 09:44 PM


what do you mean 92 is 95? and the carb is spotless I just took it apart and set the jets and accelerator pump to stock since the bike is stock.

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  • Kaw_04_250f

Posted January 15, 2013 - 03:57 AM


I have an 08 that has low hours and a friend of mine bought an almost new 2009 last summer. When i started his bike I thought it was going to throw a rod or something. It has a very loud knocking noise but runs like a champ. He has had it checked out and they say it is ok??? If it is fuel, why wouldn't an 08 have the same issue? Just wondering......

  • grayracer513

Posted January 15, 2013 - 11:22 AM


what do you mean 92 is 95?

What he means is that the manual calls for 95 Research Octane, which is different than Motor Octane, which is different than the "anti-knock index" that is posted on US gas pumps. The Research Method is used in all of Asia, Australia, and most of Europe.

Because of differences in test methods a fuel that tests at 95 by the Research Method will produce roughly the same resistance to detonation that is offered by fuels testing at 86 under the Motor Method. The US and Canada post the average of these two (R+M/2) on all gas pumps as the "Anti-Knock Index". Fuel sold in the US as 91 Octane is the approximate equivalent of 95.5 Research Octane.

  • FinchFan194

Posted January 15, 2013 - 01:08 PM


Thanks Gray!

  • vic2340

Posted January 15, 2013 - 05:19 PM


Oh ok I see thank you very much gray racer. This is to kaw 04 250, My bike knocks loud as hell and was bogging badly, I actually bought an easy adjust pilot air screw for my carb and put it in. The bike now runs best at about 2 and 1/4 turns out. The bike doesnt pop anymore but likes to hesitate while in low rev ranges. Anyways I looked up videos on youtube of my bike and 07's and 08's and almost all of the vids the motors sounded exactly the same as my bike so I guess im ok. Its just those years motors sound like they are going to blow up haha. I just hope I can tinker with the carb some more read the trouble shooting procedure and get rid of that annoying hesitation.

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