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  1. #1
    Matrix 200 suparoo's Avatar
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    Racing at altitude

    Is there any rule of thumb on what to do if you take your ski to race at altitude if it has been tuned for sea level ?

    I've got a race coming up for the Matrix that will be 1200ft above sea level. Is this enough to worry about ? The carbs are Tripple Keihin's with high speed screws. Air temp will be around 50F (winter enduro)

    Cheers John


  2. #2
    slothman's Avatar
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    Quote Originally Posted by suparoo View Post
    Is there any rule of thumb on what to do if you take your ski to race at altitude if it has been tuned for sea level ?

    I've got a race coming up for the Matrix that will be 1200ft above sea level. Is this enough to worry about ? The carbs are Tripple Keihin's with high speed screws. Air temp will be around 50F (winter enduro)

    Cheers John
    1200 ft is no big deal, the ski might a tad lean, but nothing to worry about. Maybe bump the octane +1 to prevent detonation.

  3. #3
    Trying to chase 1200 feet will be next to impossible...you can get more of a delta from the barometric pressure.

    Sudco is an excellent source for any carb parts and will have jets in just one or two instead of the usual 5's that local dealers carry. So you could go to the very next leaner main and ride happy.

  4. #4
    I'm feeling naturally aspirated today pirate33's Avatar
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    It wont even be a bump to the ski at 1200ft with the 5gal 91 to 1gal 110 mix

  5. #5
    Matrix 200 suparoo's Avatar
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    Quote Originally Posted by slothman View Post
    1200 ft is no big deal, the ski might a tad lean, but nothing to worry about. Maybe bump the octane +1 to prevent detonation.
    Quote Originally Posted by illin View Post
    Trying to chase 1200 feet will be next to impossible...you can get more of a delta from the barometric pressure.

    Sudco is an excellent source for any carb parts and will have jets in just one or two instead of the usual 5's that local dealers carry. So you could go to the very next leaner main and ride happy.
    Going to run 98 octane (ron) normally run 95 no problem. So does it lean or richen as you go up in altitude ?

  6. #6
    20 feet Boy's Avatar
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    It richen at altitude. At 1200 feet that not much. If you were dial at 5000 feet and took the ski to sea level it would be lean and would most likely blow up. That is why the race at pikes peak is hard to dial in. By the time they get to the top the bikes are blubbering. But I am no expert on it.

  7. #7
    PolarisNut's Avatar
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    1200' isn't much to worry about. If the air was cool and dry, and the baro was high, you could actually end up with a DA that is lower than your sea level riding spot. More than likely, an 1/8th to 1/4 turn in on the highs and lows will be more than enough to compensate.

  8. #8
    slothman's Avatar
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    you can also run a hotter plug (one step) that will burn the rich fuel condition at a faster rate

  9. #9
    Matrix 200 suparoo's Avatar
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    Would a good plan be to check the max rpm @ sea level which is usually 7450rpm then when I go to the lake check the max rpm again if its down lean it out a bit to bring the rpm back up.

  10. #10
    PolarisNut's Avatar
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    Quote Originally Posted by slothman View Post
    you can also run a hotter plug (one step) that will burn the rich fuel condition at a faster rate
    -1...sorry, doesn't work that way.

    Quote Originally Posted by suparoo View Post
    Would a good plan be to check the max rpm @ sea level which is usually 7450rpm then when I go to the lake check the max rpm again if its down lean it out a bit to bring the rpm back up.
    Yeah, that's a good idea...but keep in mind, when going up in elevation (especially major changes), the engine WILL be down on power, and you won't be able to recover the lost RPM without depitching the impeller. Your 1200' change should be fine though.

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