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Thread: jetting - elevation change

  1. #1
    apriliaforum Member
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    jetting - elevation change

    I'm running 270/280 main. 27.5 pilot at sea level (Portland International Raceway)

    Does the drop-a-size-for-each-2000ft hold true for the RS250?

    I'll be taking the bike to Oregon Raceway Park (ORP) on the 15th and it's at 2185 feet.

    At sea level I was running #3 clip position and had a large dead zone between 8k-10k. I raised the clip to #2 position but (for various reasons) never got a chance to get back out and see if it improved the situation. Not ideal to now be changing elevation but that's the way it is.

    If anyone has ridden at ORP, I'd appreciate knowing what jetting you were running,

    Also, as an aside, is there a good "jetting by feel" tutorial that works well to the RS250? I've owned a lot of 2T singles but never a twin.

    Thanks

  2. #2
    apriliaforum expert mattology's Avatar
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    what pipes are you using?

    Get your confidence back with Aprilia.

    caution: the use of motorcycles may be habit forming. side effects include purchasing multiple examples of the same bike, in different states of tune, different years, or different models altogether. some motorcycles may be not running when purchased. some parts are no longer available. there are rare instances where aprilias are bought over the internet and upon arrival, they are not as were originally disclosed. there is a small group of people who cannot handle two stroke engines and motorcycle maintenance. if this is the case, you may not be a candidate for Aprilia RS250's.

    Aprilia. Ask your doctor if the RS250 is right for you.

  3. #3
    apriliaforum Member
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    Quote Originally Posted by mattology View Post
    what pipes are you using?
    Pipes are the DLR which i believe were stock on the USA Cup Challenge bikes.

    Found a cleaning/repacking video here: https://www.youtube.com/user/redmonkey46/videos?view=0

    Sent from my Nexus 9 using Tapatalk

  4. #4
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    Bueller?

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  5. #5
    apriliaforum expert mattology's Avatar
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    When I ran my bike on stock pipes, 270/280 it ran fine on 98 octane unleaded race gas, but the bike was way too lazy and spit back at me a ton with avgas. avgas preferred 260/270, even 250/260 it seemed like would have been even better, but i never ran 250/260 so i don't know...

    but this was in hot weather in florida.

    I use this app on my iphone now, its worth every penny of the 3.99 or whatever i paid for it. it's called Air Density Meter & Density altitude calculator. It's awesome for making adjustments.

    once i figure out where my jetting is where it's runnign good, i look at that in my logbook, and then i make adjustments to what the calculator says. If i notice a 10% difference in relative density, that's when i am told that i would need to go up or down a jet size.

    I just did a comparison between my weather here in florida and the weather station at grass valley which is closest to where you're at, and it looks like to me, if i were there, i would not make any significant jetting changes...

    Make some comparisons between where you ran the bike last , and where you're running the bike now..

    keep a log book.. good luck!



    manually adjusting the weather data if you choose

    ST PETE Florida weather results


    Grass Valley (Oregon Raceway Park closest weather station) weather results


    So if it were me... I would probably run 270/280 on unleaded gas in the 93-98 octane range, or 260/270 on avgas.

    Get your confidence back with Aprilia.

    caution: the use of motorcycles may be habit forming. side effects include purchasing multiple examples of the same bike, in different states of tune, different years, or different models altogether. some motorcycles may be not running when purchased. some parts are no longer available. there are rare instances where aprilias are bought over the internet and upon arrival, they are not as were originally disclosed. there is a small group of people who cannot handle two stroke engines and motorcycle maintenance. if this is the case, you may not be a candidate for Aprilia RS250's.

    Aprilia. Ask your doctor if the RS250 is right for you.

  6. #6
    apriliaforum Member
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    Quote Originally Posted by mattology View Post
    I use this app on my iphone now, its worth every penny of the 3.99 or whatever i paid for it. it's called Air Density Meter & Density altitude calculator. It's awesome for making adjustments.
    So it's this app? If yes, they have a similar app in the Google Play store called Air Density and RAD Meter. Looks very similar to the iPhone version, 3 main tabs, "results", "weather" and "gps".

    If i notice a 10% difference in relative density, that's when i am told that i would need to go up or down a jet size.
    So the app tells you this? I can't see where the Android version will do this.

    So when you drop a size, are you dropping size on pilots as well as mains? What about needle?

    I just did a comparison between my weather here in florida and the weather station at grass valley which is closest to where you're at, and it looks like to me, if i were there, i would not make any significant jetting changes...
    Obviously comparing St Peterburg to Grass Valley is apples/oranges as StP is humid and so has a similar relative density but I get what you're saying. For me I want to compare Portland (sea lavel) with Grass Valley. Out of curiosity, how did you pull up the data for Grass Valley? I can't see where I can enter arbitrary locations into the Android App. It only seems to want to obtain info based on current GPS location.

    There is another app for Android called Rad Calc which seems to keep a digital log book but I can't figure out if it does anything more than this to justify the $8.99 price.
    Last edited by crazybrit; 06-08-2019 at 11:34 AM.

  7. #7
    apriliaforum expert mattology's Avatar
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    Quote Originally Posted by crazybrit View Post
    So it's this app? If yes, they have a similar app in the Google Play store called Air Density and RAD Meter. Looks very similar to the iPhone version, 3 main tabs, "results", "weather" and "gps".


    So the app tells you this? I can't see where the Android version will do this.

    So when you drop a size, are you dropping size on pilots as well as mains? What about needle?


    Obviously comparing St Peterburg to Grass Valley is apples/oranges as StP is humid and so has a similar relative density but I get what you're saying. For me I want to compare Portland (sea lavel) with Grass Valley. Out of curiosity, how did you pull up the data for Grass Valley? I can't see where I can enter arbitrary locations into the Android App. It only seems to want to obtain info based on current GPS location.

    There is another app for Android called Rad Calc which seems to keep a digital log book but I can't figure out if it does anything more than this to justify the $8.99 price.
    so i don't have any experience with the android version, but on IOS you can click the 'weather' tab and then make adjustments as needed.

    from there you can type in / adjust the values as needed - i use weather stations on https://www.wunderground.com/wundermap and you can pick grass valley for example.


    I just did a comparison of grass valley to portland just now. portland air density is 0.0759 - relative air density of 99.32% grass valley is relative air density of 92.18% . that's a ~ 7% decrease in air density.

    If those figures hold about the same, I would jet 1 size leaner going from portland to grass valley.

    for my bike in summer, I would go up a jet size if going to portland, but leave my jets the same at grass valley, lol!

    Get your confidence back with Aprilia.

    caution: the use of motorcycles may be habit forming. side effects include purchasing multiple examples of the same bike, in different states of tune, different years, or different models altogether. some motorcycles may be not running when purchased. some parts are no longer available. there are rare instances where aprilias are bought over the internet and upon arrival, they are not as were originally disclosed. there is a small group of people who cannot handle two stroke engines and motorcycle maintenance. if this is the case, you may not be a candidate for Aprilia RS250's.

    Aprilia. Ask your doctor if the RS250 is right for you.

  8. #8
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    Quote Originally Posted by mattology View Post
    so i don't have any experience with the android version, but on IOS you can click the 'weather' tab and then make adjustments as needed.

    from there you can type in / adjust the values as needed - i use weather stations on https://www.wunderground.com/wundermap and you can pick grass valley for example.
    My bad. I thought from your earlier post that you were able to enter a location (like Grass Valley) directly into the Air Density app. I didn't realize you were getting the data from Wunderground and then manually entering it. Looks like Android is the same then as IOS.

    I just did a comparison of grass valley to portland just now. portland air density is 0.0759 - relative air density of 99.32% grass valley is relative air density of 92.18% . that's a ~ 7% decrease in air density.

    If those figures hold about the same, I would jet 1 size leaner going from portland to grass valley.
    Pilot and main?

    Thanks for the info.

  9. #9
    apriliaforum expert mattology's Avatar
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    main jet for sure, possibly power jets also. my bikes are premix, so not only do i think about the atmospheric change for the pilot jet, but i also consider the length of the straightaways when sizing the pilot jet

    Get your confidence back with Aprilia.

    caution: the use of motorcycles may be habit forming. side effects include purchasing multiple examples of the same bike, in different states of tune, different years, or different models altogether. some motorcycles may be not running when purchased. some parts are no longer available. there are rare instances where aprilias are bought over the internet and upon arrival, they are not as were originally disclosed. there is a small group of people who cannot handle two stroke engines and motorcycle maintenance. if this is the case, you may not be a candidate for Aprilia RS250's.

    Aprilia. Ask your doctor if the RS250 is right for you.

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