Xr650l jetting and mixture screw

Discussion in 'Thumpers' started by rangecon1976, Jun 8, 2013.

  1. rangecon1976

    rangecon1976 Adventurer

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    Ok guys I just returned from a trip completing the TAT to the Colorado border and a little further. I live at about 1600 feet and my 2008 xr650l has the smog crap removed, a supertrapp with 8 discs I think , Dave's mods 55/158 jets, and a uni filter. While in co around 5500-6000 feet I was running rich and getting about 30 mpg, I usually get 40 and sometimes higher. This led to some fuel issues (ie me running out.... Several times) which my buddies thought was hilarious.:rofl

    My question is this how much leaner can I make my bike with only the mixture screw?? I did not try this then because it seemed to be running ok just a little rich. I know I need to re-jet before we continue on , I am just curious if I get in the same predicament can I help the situation by using the mix screw and still maintain a good running bike or is it best to just re jet that night at camp?

    Also I wonder if I could help the situation by adjusting discs on the supertrapp ?

    Bottom line is I am just wondering if I can best guess jet the bike for what I think I need, then adjust while on the trail and elevation is changing greatly ?? And keep my mpg a little more like normal.

    Sorry it's so wordy......thanks ahead of time!!

    Dave
    #1
  2. AZ TOM

    AZ TOM Long timer

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    I would go with a 52 pilot & leave it alone.
    #2
  3. CNRED

    CNRED It'll be OK

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    +1 Tom.
    Messing with the screw jet is not going to get you where you need go. Your fuel milage is not determined with the screw jet. Evaluate your Main jet, I would start with one step leaner and keep leaning until you get to the performance and mileage you are looking for.
    Velocity carbs are tricky. there is a happy place between fuel, air and exhaust. You should be able to adjust some of the problem out with your Supertrapp, add or subtract disks to acheive the desired effect. Your Supertrapp will help a ton to redemy "Altitude Sickness" at those elevations above 7000 ft.
    #3
  4. rangecon1976

    rangecon1976 Adventurer

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    Bump
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  5. rangecon1976

    rangecon1976 Adventurer

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    bump
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  6. señormoto

    señormoto Supermoto Abuser

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    hey guys... I'm living in Telluride, CO and we're at 8,750'. All of the passes (Imogene, Engineer, Ophir, and others) are 11,000 to 13,000'. Jetting here for the XR and other bikes SUCKS.

    Here's my advice to OP: this all depends on what other mods you've done aside from Dave's carb mods. First, you've already de-smogged, but did you take out the airbox snorkel? If you do that you will probably not need to change jets. Here is why:

    The stock main jet is a 152 Keihin, which is a 140 dynojet. If you have a 158 keihin that's a 144 dynojet main. I am running de-smogged, no snorkel, UNI filter, and a FMF Q4 pipe and my jetting has *mostly* stabilized where it will start up and idle nice and smooth with a 160 dynojet main (178 keihin).

    So my advice if you are going over the TAT in the rockies and doing high passes is to rip out the snorkel and leave your current main jet in. That will give the bike much more air and balance out the richer main you are running.

    If you are already de-snorkeled and still having issues then run over to a smog center and ask them if you can run the bike on their machine (with the tube stuck in the exhaust pipe) and then adjust the fuel screw clockwise until you bottom out and see what the reading is; if it's still over 13.2 then you have to change your main. If you can get it under 13.2 with the fuel screw and you aren't going higher up in elevation then leave it alone and use the fuel screw and the supertrap disks to tune it accordingly.

    If you're up high and find yourself needing to adjust the idle screw a lot to keep it running, you need to rejet. If it's overheating on high passes and you're not lugging it or carrying tons of luggage, you need to rejet. If it stutters and dies on high passes, you need to rejet.

    References: http://www.jetsrus.com/FAQs/FAQ_mikuni_vs_dynojet_vs_keihin_sizes.htm
    http://www.carcraft.com/techarticles/116_0402_innovate_air_fuel_ratio_meter/
    #6
  7. joexr

    joexr Banned

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    Or he could ask somebody that actually knows what they're talking about.:deal
    #7
  8. Bell driver

    Bell driver Been here awhile

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    Too much fuss and guessing.
    Install a bung for a Lambda sensor into the header, buy or borrow an air/fuel meter and jet according to the findings.

    This is what it can do, the bottom graph is the A/F ratio.
    [​IMG]
    #8
  9. señormoto

    señormoto Supermoto Abuser

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    Sounds good. Let me know when you know what you're talking about, because so far you've had all the right answers for the OP. oh wait... no, you haven't have you? :lol3
    #9
  10. señormoto

    señormoto Supermoto Abuser

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    Agreed, good suggestion. I was looking at a similar kit for a different bike and, although it takes a trip to the welder to get the bung installed, it's the best solution and removes all of the guess work. This is the only full kit I've found for carb'd bikes but maybe there are other good ones online: http://www.amazon.com/Innovate-Motorsports-3844-Complete-All-In-One/dp/B004MDT8MW/

    Not bad for $160, add a bung for $8 and it's all ready to go.
    #10
  11. mcma111

    mcma111 Long timer

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    Like this?
    [​IMG]
    #11
  12. señormoto

    señormoto Supermoto Abuser

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    Looks good - minus a little rust over in that one area ;)

    I can't tell if that plug is the iridium style? I have one of those sitting around that I've been meaning to put in myself but haven't gotten around to it.
    #12
  13. katbeanz

    katbeanz earthbound misfit, I

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    http://www.advrider.com/forums/profile.php?do=ignorelist :deal

    Carry on, I see Imogene is open. :thumb
    #13
  14. señormoto

    señormoto Supermoto Abuser

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    #14