Aftermarket throttle kit?

Discussion in 'CT90, CT110, ST70, ST90 Discussion' started by Thomas H., May 7, 2018.

  1. Thomas H.

    Thomas H. New Member

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    Hi,

    I'm considering to do something drastic with the throttle on my soon to be build Honda ST50, - due to the famous "cruise control", AKA sticky throttle.

    Do anyone know of any throttle kits/conversions kits, that'll fit the Dax?
    I've read about a kit from Motion Pro and Kitaco as well, but not quite sure that I've located the correct items.

    If not it appears I'll be trimming the lip, greasing the movable parts, and perhaps adding a return spring inside the handle - and only hoping for the best.

    On a sidenote: Is it normal that when the screw that goes through the throttle pipe and the throttle stop is screwed all the way in (as far as it'll go), it still doesn't sit flush with the top of the throttle pipe, meaning that whenever you turn the throttle, the throttle stop moves a milimeter or so, because it ain't tightened all the way down?

    Kind regards,
    Thomas
     
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  3. racerx

    racerx Administrator
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    Aftermarket, clamp-on/external throttle assemblies are readily available, take your pick. 7/8" diameter handlebars are beyond common. If you want something that works a lot better than the 6v-era internal throttle setup, be prepared to spend some cash. The biggest issues behind the old, dreaded, "CT70 cruise control" are a weak return spring and binding, usually due to cable damage/dirt/rust...cuased by neglect.

    Start with a minty-new throttle cable assembly, a cleaned & properly lubed twist grip assembly and you may actually restore the original self-returning action. Granted, these things were never state-of-the-art, even back in the day. That said, they did work better than most do, at this late date. Believe it, or not, the internal twist grip assembly improves with use. The helix & slide both break-in and those smoothed contact surfaces have less friction/binding. The new, OER, throttle pipes have been six shades of shitty; they all have burrs and the latest batch I sourced (circa 2014) have the helix incorrectly clocked inside the pipe. The helix can actually be launched off the trailing end of the slide...leaving the throttle stuck wide-open.

    As you may have seen, firsthand, repop handlebars come fitted with plastic end plugs. The RH one should be removed. Also, OER vinyl grips fit a little differently than the vintage originals. During installation, you want to stop just before the end of the vinyl can make contact with the end of the handlebar. The open end is a little trickier to figure out and requires some artistry. If you completely remove the lip, you run the risk (small) of dirt getting inside the assembly; that's easy enough to deal with, via periodic cleanings. However, the really annoying side effect is the rattling if too much is removed. Let the bike sit, idling, to warm-up the engine and you'll learn firsthand what this means. Armor-All does an amazing job making polymer items slick; a little bit, applied to the end, plus some minor lip surgery makes a bigger difference than you might expect. As for lubing the metal parts of the twist grip assembly, use a thin, lightweight, grease...lithium grease, or Lubriplate (if you can source it), is ideal. Wheel bearing grease tends to be too thick, resulting in binding...especially in cooler weather. Lastly, the throttle return spring can be replaced, or stretched a bit. It is sometimes possible to use two springs inside the carb slide; I'm not crazy about that setup. Mo`better, imho, to just source a stronger spring.
     
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  4. Thomas H.

    Thomas H. New Member

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    Hi racerx,

    Thanks a lot for the thorough reply.
    I have only a few more questions that you perhaps could help me find the answers for;

    1. Any specific recommendations for complete throttle kits that work (should you have any experience), and that should go with my model?

    2. I bought new parts, all OEM - might now however be quite the same quality as Honda build back then - can't say. Is the good advice about stopping just before the end of the vinyl makes contact with the end of the handlebar during installation also relevant when installing OEM handlebars, or only when installing OER? Same goes for the lip surgery. If these suggestions also applies to the OEM parts, what kind of surgery do you do? Trimming only half part of the lip in order to avoid some of the friction, but still making sure there won't be any rattling?

    3. I've used a dry PTFE spray - this: https://uk.rs-online.com/web/p/lubricants/7577134/ - read that some had luck with something like that, - but might look into lithium if you believe that to be better, your experience taken into consideration.. And it seems like you've got lots of that ;) Appreciate all the answers that you've given me so far.

    4. Is the phenomenon that I described in my sidenote normal? Afraid that it'll cause friction and wear to my otherwise fine metal handlebars, causing rust etc.

    I've attached a few pictures showing how I've actually trimmed some parts of the lip, and how the screw in the throttle stop/throttle pipe protrudes slightly, and aren't fastened all the way down - can't make it go any further. Might be completely normal, but I'm not quite sure.
    Waiting for my cylinder head to arrive, so I can mount it and attach the throttle cable in the other hand.
    It's however not even possible to close the throttle by just pulling the inner cable with my hand, doesn't move an inch.
    I can however move the throttle itself back and forth by hand, quite easily, - but not exactly buttery smooth.

    I do apologize for all the questions related to something that surely should be quite simply!
    Also you might notice that there's a tiny bit of rust on the outside of the throttle pipe.. Which most likely have been caused by the advise of using soap water when mounting the vinyl handles :/


    Kind regards,
    Thomas
     

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  5. racerx

    racerx Administrator
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    Looks like the retaining screw may be crossthreaded. It's standing a little too proud of the inner collar. If it's just a matter of the screw being 1-2mm too long, a few seconds at the grinder should cure that.

    Try removing the vinyl grip, altogether, then get the throttle return action sorted. Afterward, reinstall the vinyl grip; if throttle action is degraded, there'd be no question that it's the grip and the cure would be eliminating...or at least seriously minimizing...vinyl-to-metal contact.

    FYI, since 2000, OER throttle pipes have had various Q/C problems. At best, the internal helix will have burrs...which results in notchy throttle action and really interferes with the return. I've been running the same one, sourced back in 2001. After ~24,000 miles, it's nicely worn-in...it took close to 10,000 miles (as best I can recall) to wear down the burrs enough to realize smooth action.

    I would not recommend a dry film lubricant for the throttle assembly...not enough "body". Thin, lightweight, grease with good high-pressure characteristics, is needed.
     
  6. Thomas H.

    Thomas H. New Member

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    Hi racerx,

    Sometimes I apparently over complicate things ;)
    Took it all apart and realized that the throttle screw was indeed crossthreaded in the throttle holder. Managed to "re-drill" the threads with some WD40 and a plier. Afterwards it was possible to screw it all the way in. While I were at it, I relubed with some lithium grease, and removed a bit more of the inner lip. A few new pictures attached.
    It's going a lot more smooth now (naturally), and I can't wait to get the proper top set for my carb, so that I can test it out properly.
    The first top set I was supplied had a too long swan neck, basically causing my throttle to stay open all the time.
    Thanks a lot - really appreciated!

    PS: It appears that the quality ain't what it used to be, so guess I'll have to ride quite a few miles like you did before it's top notch - but it's definetely much improved.

    Kind regards,
    Thomas
     

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