Jetting for altitude??

4 replies to this topic
  • WB450

Posted August 06, 2007 - 12:45 PM


If you know your going to be riding at a higher altitude your next ride, will take the time to change your jets? If so how do you get it right? If not what do you do?:excuseme:

  • grayracer513

Posted August 06, 2007 - 12:48 PM


How much altitude change are we talking about?

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  • WB450

Posted August 06, 2007 - 12:55 PM


Home is about 2,500 and a ride could go up to 6,000 throughout the course of a day.

  • grayracer513

Posted August 06, 2007 - 02:37 PM


I rarely rejet beyond a simple adjustment of the fuel screw, and I run mostly at altitudes ranging from 4000 ft to below sea level (that's right). That's a range slightly greater than what you list. A four-stroke will tolerate being off of perfect jetting far better than a two-stroke, and better than most people will give them credit for. If your jetting was "perfect" at 3500-4000, your bike should run OK throughout that range.

What often happens, too, is that as the altitude increases, the temperature drops, and this offsets some of the altitude gain.

For a very rough approximation, figure that your main jet should be corrected by about 1% for each 1000 foot change in elevation, and 1% for each 10 degrees (F) in temp. So if you have a 165 now, and you go up 3000 feet, multiply the 165 by 0.97 to get 160. But if it's 90 where you are, and it's 80 up there, then multiply the 160 by 1.01 for 162 (rounded).

  • WB450

Posted August 06, 2007 - 03:31 PM


Great info thanks!

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