? about jetting maybe?

4 replies to this topic
  • sawyer1

Posted November 04, 2008 - 07:11 PM


So i have a 2001 yz 426 the bike seems to run fine unless you get on it after being in mid range power. It will start to bog or miss im not really sure, unless i clutch it to bring the rpm's up before getting on it. Im lockated at 3200 feet and i bought the bike from a guy that is located around 7000 feet. Could that be the problem? It was recently built with a big bore kit and 13.5.1 compression. about 5 hours ago could it not be broke in yet?


  • grayracer513

Posted November 04, 2008 - 07:25 PM


It could be that the bike is now too lean, because of having been jetted for higher altitudes.

Check the Jetting DB and then read through this:


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  • sawyer1

Posted November 05, 2008 - 04:20 AM


Thanks grayracer513 for such a quick reply that info should help.

  • sawyer1

Posted November 07, 2008 - 03:07 AM


I was also wondering if my fuel could cause this problem since i was riding it with 85.5 octane. I know it should be higher octane level should i go with 91 and a octane boost?


  • grayracer513

Posted November 07, 2008 - 05:46 AM


US pump premium (91-92) is all that is required. 85 is too low. The fuel may be a part of the problem, especially in a bike jetted for a much higher altitude, if it contains a lot of alcohol, but the octane isn't what your problem comes from.

The manual calls for 95, but that's by the Research method. The US "Anti-Knock Index" is derived by averaging the Research and Motor octane numbers, and a Research Octane Number (RON) of 95 is roughly equivalent to 90-91 AKI. Spending any money chasing higher numbers is completely unnecessary, and a total waste.

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