High Altitude Riding


8 replies to this topic
  • Flosi77

Posted July 27, 2008 - 02:26 PM

#1

Ok so i have a 04 yz450f and it runs like a complete turd up above 7,000ft the thing is a i'm going to be riding between 7-12 thousand ft next week and am lookin at trying to help it out a little so i can enjoy myself on the trail. ANyways i have started by dropping my main jet froma 172 to a 165....any other suggestions?

  • grayracer513

Posted July 27, 2008 - 02:51 PM

#2

In what range of altitudes do you normally ride?

  • Flosi77

Posted July 27, 2008 - 02:54 PM

#3

my home is around 1,200 and i typically ride up high like i am going to this week or down in mojave

  • grayracer513

Posted July 27, 2008 - 03:04 PM

#4

For a 8000-10,000 foot increase in altitude, assuming the temperature is roughly the same, multiply your normal home/Mojave main and pilot jet sizes by .91 to .93, and use the nearest size (Your 172 would be a 160-157)

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  • Flosi77

Posted July 27, 2008 - 03:09 PM

#5

thanks....yeah i thought 165 was still to big...guess i'll make some last minute changes before i head up tuesday

  • grayracer513

Posted July 27, 2008 - 06:16 PM

#6

Don't forget to drop the pilot by the same factor.

  • rdefonce

Posted July 28, 2008 - 08:48 AM

#7

Don't forget to drop the pilot by the same factor.


Good suggestions for hi-alt. one thing I notice you didn't mention is changing needle clip position. I have always moved it one clip leaner when going "up high" (home altitude only 500ft, hi-altitude 9-13k ft) but do you think that may not be necessary?

  • grayracer513

Posted July 28, 2008 - 08:53 AM

#8

Not always, and not even the majority of the time. The needle is a secondary metering device that modifies the flow of fuel after it is first metered through the main jet, so it has less fuel to work with when there is a smaller main.

However, every engine is different, and any given one of them may still be too rich at part throttle even with the smaller main. If it blubbers at a steady throttle between 1/4 and 3/4, then it's asking for less fuel, and you should drop the needle.

  • rdefonce

Posted July 29, 2008 - 08:26 AM

#9

Not always, and not even the majority of the time. The needle is a secondary metering device that modifies the flow of fuel after it is first metered through the main jet, so it has less fuel to work with when there is a smaller main.

However, every engine is different, and any given one of them may still be too rich at part throttle even with the smaller main. If it blubbers at a steady throttle between 1/4 and 3/4, then it's asking for less fuel, and you should drop the needle.


Hmmmm . . . next time I may leave the needle alone and change only the main.
I definitely don't experience any blubbering between 1/4 and 3/4 throttle.





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