Airhead Spliltter Throttle VS 2 Cables

Discussion in 'Airheads' started by Wirespokes, May 3, 2008.

  1. Wirespokes

    Wirespokes Beemerholics Anonymous

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    I prefer the style of throttle that pulls two cables from the bar rather than the other that pulls just one.

    For a long time I'd been wondering how to convert mine - it's a 77S that was converted by a PO to handlebar mounted Master Cylinder. But since it needs new cables I wanted to convert to the dual cable system first.

    Finally I saw on Snowbum's site that the 1985 to 95 airheads returned to the dual pull system and that was just the info I needed. I was beginning to think I would need to do some fancy machining to convert this single pull to a dual.

    I've got two questions: one is that snowbum says he prefers the single pull system using the splitter. I don't understand that. He doesn't elaborate, but for one, the splitter is added complexity that doesn't seem to help. Any idea why he would prefer that style? Also, since BMW returned to the dual pull system after four years tells me they found that system better as well. What are your thoughts on this?

    I'm considering mounting a set of Dellortos on this bike and with a dual pull system could get standard 90S cables rather than have something special made up. But even if I don't do that, I just don't like those splitters and prefer the positive pull to each carb rather than something in between with added friction.

    Is there something I'm missing? I can see that it's a good idea having less cables to the controls which would translate to less resistance turning lock to lock. But other than that, I see nothing else on the positive side of the ledger. And, if you happen to have one of these controls you'd consider passing on to a good home, let me know.
    #1
  2. lkchris

    lkchris Albuquerque

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    It's my experience that the one-into-two system is a big improvement.

    Every year or so, I put my carb balance checker on just for fun--my carbs always stay balanced. Lot less cable to stretch. Can think of no earthly reason to prefer the dual-cable setup.
    #2
  3. benway

    benway Been here awhile

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    iirc the S/dellorto throttle cam is different than the stock /6, because of the heavy pull on the slides vs bings
    #3
  4. pommie john

    pommie john Long timer

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    All the splitter boxes I've come across have a limited range of movement of about 36mm. If you have a 38mm slide carb like on the R90s you need the cables to move at least 38mm ( and a bit more for free play) so a splitter that only moves 36mm ain't no good.
    #4
  5. Wirespokes

    Wirespokes Beemerholics Anonymous

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    I didn't know that about the limited splitter range of movement. Guess I'd have to convert over. I'd also thought the throttle gears were the same, at least for the larger displacement bikes. I'd heard the 32mm bings used a different gear than the 40s, but other than that I'd assumed they were all the same. I'll have to research the parts fiche.
    #5
  6. AntonLargiader

    AntonLargiader Long timer

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    I agree, the splitter system stays in sync better especially as the handlebar is turned. It's slightly more fussy to set up, it has more parts, and the splitter gets all rusty and cruddy when the boot rots away (which takes about 8~10 minutes), but when the parts are in good shape and the splitter is positioned so as to allow nice cable bends, it works well and holds sync really nicely.

    The throttle cam gear history is pretty convoluted and I haven't fully deciphered it yet. What little I know about it is on my website under the 40mm stuff, on an orphan page:

    http://www.largiader.com/articles/40mm/

    There are a whole lot of throttle cams. I haven't listed them all yet.
    #6
  7. Stagehand

    Stagehand Imperfectionist

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    i believe my PD has a dual-throttle, and splitter-choke setup.
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  8. opposedcyljunkie

    opposedcyljunkie Heavyweight Boxer

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    same here...
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  9. datchew

    datchew Don't buy from Brad

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    Ditto on my 89 GS. If you clean and lube the internal slider of the choke 1 into 2 setup, then you can cocoon the outside of the plastic cap with clear silicone and it lasts alot longer. When you want back in, simply cut and peel.

    :1drink
    #9
  10. Wirespokes

    Wirespokes Beemerholics Anonymous

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    All of the bikes after 84 have the two cables throughout. The difference between the GS and the others is that the GS used the K bike controls for some reason unknown to me. Perhaps to make it special with different switches? The GS (and R100R) have a square master cylinder reservoir and that's one of the distinguishing features.

    Thanks Anton - that's some great data.
    #10
  11. opposedcyljunkie

    opposedcyljunkie Heavyweight Boxer

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    The R100R as well...
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  12. AntonLargiader

    AntonLargiader Long timer

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    Actually the R100GS only used those controls '91-on, but had the twin throttle cables from the beginning in '88. I like the Kontrols better, so I will probably (this is about 18th on the list, right after cutting off that R65 SH for you) convert my '88 to them when I repaint it and bump the compression. Hmm, if I dropped everything else I bet I could get that done in time for XPLOR Blue Ridge....

    BTW I was hoping to get Stagey to cut that frame up for you but forgot to twist his arm.
    #12
  13. boxerboy81

    boxerboy81 Stay Horizontal

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    Is there a trick to removing the two lower cables from the splitter?



    .
    #13
  14. Wirespokes

    Wirespokes Beemerholics Anonymous

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    It's been a while since taking one of those apart, but I seem to recall needing the top one (from the throttle) free, which will allow the internals to slide out far enough. You may have to screw in the adjuster also to give more slack.
    #14
  15. boxerboy81

    boxerboy81 Stay Horizontal

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    Thanks.
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  16. supershaft

    supershaft because I can

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    I am in the same boat you are in Ws. I am running Dellorto's so I pretty much have to run two separate cables. I would run the splitter otherwise. They stay in sync a lot better with the splitter. I think BMW quit using the splitter because with the stock setup they almost instantly fill with grit from road wash running down the cable and into the boxes. The very simple solution is to put some electrical wire shrink tubing over the single cable before you assemble the splitter. Set it up and then slide the shrink tubing over the cable adjuster and shrink it on the cable. I know from experience that they will stay perfectly spotless inside for tens of thousands of miles and tens of years thusly modified. I have always put a dab of lithium grease and Tri Flow in mine. Works perfect.

    Running Dell's? I am pretty sure they need a different throttle cam to open up all the way although I do think the longer travel cam opens the slide up too much. That might hurt more than it helps but I don't know. I would check it out on a flow bench if I had one. I am pretty sure one 40mm cam has a lot more progressive pull than another that is available. I filed my velocity stack threads about half way down (you can use the width of the threads as an indicator in order to keep the project round) and then the later model snorkel tubes fit perfectly right on to the carbs minus the convoluted R90S setup with radiator hose on it.

    Like I always try to help with, don't forget that R90S stock jetting is way rich. The pump can't be turned off enough without completely disconnecting it but that requires completely rejetting just off idle. My bike with a sport cam, mild port work, and Staintune sport mufflers made more and more power until I got down to 130 mains. If I ever mend up I can't wait to see what it will take now with some serious port work (still not flowed however), 44mm intakes up from 42's, and dual plugged with a theoretical 10:1 compression ratio. I have 140's in it right now just to be safe during brake in. I won't be surprised if I end up right back with 130's but we shall see.

    Limited splitter range of movement? I have never tried opening up a Dell with a splitter but I would think it would work? Both 32 and 40mm carbed bikes use the same splitter.
    #16
  17. Wirespokes

    Wirespokes Beemerholics Anonymous

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    Good points SS. It appears the 90S throttle cam (for use with Dels) is the same as the RT, RS and S with the 40mm Bings. So no problem there.

    I do have a dual pull control (no splitter) so don't have to worry about that either. I haven't noticed the dual cables going out of synch any sooner than the other. And your observation on the splitter possibly not providing enough length for the Dels isn't something I'd even thought about. I just like the simplicity of the system without the splitter. One thing I do like about the splitter system is there's only one cable flexing when turning = less resistance and less mass routed through an already tight space.

    Currently I'm looking for a set of Dellortos - probably PHF 34mm or 36mm - to run on my 850 R65. It's got 34mm flat slide mikunis currently but think I'd like to try the Dels. Anyone got a set they'd like to sell?
    #17
  18. Voltaire

    Voltaire Titanium and Ceramic Hipster

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    I replaced the splitter set up my Ducati many years ago with dual cables and it holds tune very well, my Norton on the other hand has a splitter and doesn't....personally I'm with less is more as far as interfaces go.
    I'm building a 900 BMW track bike and using a set of 36mm Dells, The inlet to the 900 heads is 36mm and a friend turned me up some adapters .looks good so far..with a bit of luck I can use the std air cleaner tubes.
    Also using a Tommaselli Twin 1/4pull throttle as I don't like the geared one....the KISS principle......although I need a separate starter button.
    The 36 mm carbs were used on Pantahs.Bevel Heaven sell the carbs, I got the rebuild kit from the UK.
    I used R90s jetting as the start point but sounds like it may be too rich.
    #18
  19. Airhead Wrangler

    Airhead Wrangler Long timer

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    But you don't have to pull a slide the full height of the throat on the bings. You're just turning a lever to open butterflies. A 40mm slide carb will NEED about 38mm of cable pull to open fully due to the fact that the slide is cracked open just a little at idle to set idle speed. I'd want to be able to pull at least 42mm of cable just to allow a little free play.
    #19