Jetting advice: CPR air filter on 950

Discussion in 'Crazy-Awesome almost Dakar racers (950/990cc)' started by randel, Sep 7, 2012.

  1. randel

    randel Been here awhile

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    I placed an order for CPR dome filter for 950SE and would like to have some advice regarding jetting.
    I know that some information is in general CPR air filter thread, but it's quite difficult to find from several pages and hopefully there is also some new information since then.
    Located at sea level and using 2-1 Acra exhaust with insert, I assume I would start from
    main jets 175front/180rear
    stock needle 3rd clip
    what about IAJ etc?
    I currently have H2W kit installed.
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  2. Stumpalump

    Stumpalump Been here awhile

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    How is it running with your current jets?
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  3. blublapp

    blublapp Adventurer

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    If you are running a CPR/ITG Filter, you don't need different main jets for front and back cylinder.
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  4. Vassily28

    Vassily28 TheFrenchCanadian

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    Are you using an UNI prefilter with H2W kit? If yes and you remove it, you'll have to change the main cause you're probably have somthing like 148-152.

    Even with the CPR, i think 175-180 is way too lagre mostly cause of you're 2-1. When you Akra 2-1 do you talk about a complete Akra header 2-1 system or only a standard 2-1 with an Akra exhaust.

    The standard 2-1 with an AKRA will be the most restrictive part of your system, not the air intake just like with the UNI prefilter. So maybe you'll have to use 155-160 or 160-165 main but probably not bugger than that. Somebody with a 2-1 and an OEM or DNA filter can lead you on that.

    I think that most of your gain will be in the LOW to LOW MIDDLE rev. cause the back pressure in the exhaust will raise faster. You're gonna have to adjust IMS, stock IAJ and maybe clip on needle.

    My 2 cents.:wave
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  5. Navin

    Navin Long timer

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    Check my thread on CV carbs with K&Ns, I left my H2W jetting and went up on the main to 170 sumthing as I recall. I had a 2-1 with Q4. Picked up power everywhere.
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  6. mousitsas

    mousitsas Long timer

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    Why?
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  7. randel

    randel Been here awhile

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    I have original header converted to left side 2-1 with Acra exhaust.
    Currently I run H2W with prefilter, main jets 148/152. I know it's way to lean for CPR filter.
    #7
  8. blublapp

    blublapp Adventurer

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    An austrian tuner tested this out on the dyno. It's necessary because of the construction form of the original airbox in which the rear cylinder gets more air, so more fuel is needed too.

    he sells open airboxes too and gives out this information.

    my setup with an ITG filter (same as CPR) is 155/155 mains at present.
    #8
  9. mountain eagle

    mountain eagle terrorist

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    I'm in Denver, 5280', and was running 155/160 and am about to put 165/165 in for a test.

    At least it only takes me 30-40 minutes to do the job now :clap
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  10. Balsta

    Balsta Been here awhile

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    About same main jets front and rear when using CPR (or other similar concepts),

    This is interesting stuff if correct and perhaps there are other inmates with skills to approve/disapprove on this.

    Actually, I have an oval K&N (similar concept with respect to air flows) with 175/180 on the SDR motor since 35000 kms. Exactly same nice light brown color on both plugs.
    #10
  11. mountain eagle

    mountain eagle terrorist

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    True I'd love to get that from multiple sources or someone I already trust. In the meantime I just dropped the 165's in and will ride it for a few miles and see how things feel, then see how the plugs look.
    #11
  12. mousitsas

    mousitsas Long timer

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    I did suspect that the rear larger main has nothing to do with operating temperatures, but its airbox/exhaust related....Thanks!
    #12
  13. Sporting Wood

    Sporting Wood I

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    The restriction in the airbox is the snorkel at high rpms. Bigger mains fix this, and are absolutely necessary using the airbox and even more so without. The first jet you set in tuning is the main, and its done at wide open max rpm. All the others are adjusted down to accept the larger main...This the difference between properly tuning the carbs and not.

    My experience with the 950, which is extensive, indicates there is absolutely no difference between front and back, temperature, egt, o2, etc... I have ran 170 mains front and rear in the box for 5 years. My bike is jetted near perfectly, outruns every other buddy with a 950, and returns 40mpg. o2 from either cylinder always registers between 14 and 17.

    I just made a filter like these, not the cpr, but the same filter element on an aluminum baseplate, and am starting with 175 mains, tweeking the bowls a touch leaner by lowering the floats. These carbs tend to have an annoying tendency to suck fuel from the main when it should be drawing off the slow, so compensating adjustments must be made with the float and the screws. My floats are already a mm leaner and my screws are at 2 turns. Another half mm and a half turn in might do it but I'm running it to evaluate first.

    To the op, if your swapping from the h2w prefilter jet setup to this, don't forget to swap your airjets back to stock!
    #13
  14. mousitsas

    mousitsas Long timer

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    Interesting thoughts....but why do you say that the snorkel restricts the airbox? The inlet snorkel surface area is clearly larger than each individual carb inlet. Also, the 990R can happily put down 110+bhp with an identical airbox-snorkel.
    Also, what problems do you expect if the H2W base jetting (plus larger mains) is used with a CPR filter?
    #14
  15. Sporting Wood

    Sporting Wood I

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    From lots of dyno time, the snorkle restricts airflow into the box. Simply taking it off makes a huge difference in top end, this after upsizing mains. In stock condition, the first thing to run out are the mains. Factory mains are still lean even with the snorkle on. I assume the 990R makes its higher top hp numbers from either/ or both more fuel flow through the injectors or higher rev limit, greater displacement...dunno. I have a 950. Simply put, an airbox equipped 950 benefits from a bigger main, its smaller fueling ability being the top end restriction in stock form, a 950 without an airbox benefits far more, as the next restriction caused by the snorkle is eliminated.

    In regards to using h2w's kit intended for the prefilter, this would be a total donkey show. That system relies on greater vacuum and less atomization. The airjets will be way off, really way off, and the mains beyond dangerously small and lean. I'd not be at all surprised to see a seized motor as a result! I'm certain Ken has warned against this, repeatedly. Shifting to a tune with greater airflow, less vacuum and better atomization is totally, completely different, and require totally different settings.

    Also, the stock needle has to go!
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  16. mountain eagle

    mountain eagle terrorist

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    In just the H2W set up?

    Or in the CPR set up?

    or in any setup to get the most out of the carbs?

    and then where would one source a different needle?

    Heading out now to run in the 165's and see the plugs look........
    #16
  17. mousitsas

    mousitsas Long timer

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    Well, I will report first hand tomorrow when I get to ride my previously H2W jetted SE, with 160/165 mains and obviously the snorkel in place of the prefilter. But various people have reported that the bottom H2W jetting works fine both with CPR as well as pod filters, as long as the mains are correct. Which sounds logical to me since at small throttle openings , the restriction of the filters combined should not make a difference compared to the stock setup.

    I still cannot understand why a snorkel that has larger inlet area than the carb inlet can restrict the flow (as far as top power is concerned) it makes no sense to me. I don't dispute anybody's experience, but it is a mystery to me nevertheless.
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  18. Sporting Wood

    Sporting Wood I

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    IIRC, we developed what became the H2w kit with the stock needle and the FP needle. I ran the FP version, lots of guys also used the stock. I don't think its as important. I noticed though, that in an open breathing setup that the FP needle really shines...and imho, is a necessity to get the transition from slow jet to main to work well. I found that suddenly dumping the throttle wide open with the stock needle would produce a seizure, the motor coughing and wheezing until it spooled up.

    Good luck with that. :lol3 I tested airjet combinations on k&n pods...back in '07. I know what I came up with on the dyno, real world, and through the use of an onboard o2 meter...after many hours and many different settings. YRMV
    #18
  19. mousitsas

    mousitsas Long timer

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    Well well well, luck was excellent indeed. Bike works flawlessly, bottom and midrange is identical to the prefilter setup. Top end is stronger as expected, I suspect slightly rich with the exhaust inserts (and summer temperatures), will have to try without them at some point as well as a DNA filter.

    For the record, 950SE
    Jetting is H2W sans prefilter with snorkel, stock airfilter/airbox and 160/165 mains
    Akras with large inserts
    30C @ sea level
    Nothing lost compared to prefilter setup gained a bit power on top of the rev range.
    #19
  20. mountain eagle

    mountain eagle terrorist

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    FP version? What's FP?
    #20