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Thread: Finding a Weaker Carb Return Spring

  1. #1
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    Default Finding a Weaker Carb Return Spring

    I've decided that the return spring for my carb rack is too strong. After a few hours of riding, my wrist gets really sore. In a certain sense, it affects "performance" since it's harder to flick the throttle open. I've ridden cross country on this bike and so it's not a matter of just "riding more to build up muscle" - after 6 weeks riding ~200 miles/day, my wrist still ached at the end of each day. On my GS450 and GS550, the throttle feels great - easy to pull and snaps back quickly. On the GS750, it snaps back quickly but is noticeably more difficult to pull.

    Are there any known drop in replacements? Sadly, the one from my GS550 is much shorter or I would have just plopped an extra I have in.
    1980/1981 GS450 - GS500 Cylinder + Piston Swap - "De-L'ed", custom seat, CB350 bits, 18" rear, etc.
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  2. #2
    Nessism's Avatar
    Nessism is offline Forum LongTimer GSResource Superstar
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    What about a throttle friction device?

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    Hmm interesting - Wouldn't that make it harder to open the throttle, needing to overcome both the spring and friction force? It would make for easier cruising.
    1980/1981 GS450 - GS500 Cylinder + Piston Swap - "De-L'ed", custom seat, CB350 bits, 18" rear, etc.
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    Suzuki probably erred a bit on the strong side just to be careful with their design. On the older carbs the return springs tend to be stronger than you'd think preferable, but there's a good reason for that.
    Having said that, I fitted a pair of lighter springs in the VM34s on my XS, with no bad results. There's no pull-shut cable on those either, so I'm entirely dependent on a free linkage, working spring and quick kill-button reactions in the event of a stuck throttle.
    Have at it, and just be wary of the downside.
    Last edited by Grimly; 09-11-2020 at 03:44 PM.
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    I use one of those cramp busters that attaches to the grip. It works well. Cheap enough to try before going thru the headache of messing with springs.

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  6. #6
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    I messed around with springs on the 78 1000 (probably the same as yours). At anything noticeably less than stock it doesn't snap shut as it should....

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    Quote Originally Posted by dorkburger View Post
    I use one of those cramp busters that attaches to the grip. It works well. Cheap enough to try before going thru the headache of messing with springs.
    If it were <my> bike, I would not care how much the headache would cost,
    I would find a spring LONG before using one of those evil devices.

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    Or you could use a more appropriate technique to grip the throttle grip.
    ON long trips I use my thumb and index in a light wrap around the tube housing while applying pressure onto the tube with the palm.

    Plenty of friction and very little effort. and alterable in a split second.

    I get the feeling you are on task constantly and there is no way a hand wrist forearm can do that for hours.
    While the factory spring grip etc are a constant the anatomy of the rider is variable.

    Its akin to telling a person to fret a guitar in a way that hurts them when they may be able to do it differently than accepted normality. Differently but no less effectively.
    1983 GS 550 LD
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  9. #9
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    Quote Originally Posted by salty_monk View Post
    I messed around with springs on the 78 1000 (probably the same as yours). At anything noticeably less than stock it doesn't snap shut as it should....
    I'm not sure of the physics involved, but I tried modifying the spring on a 78 750 and a 79 850 and found that when you run high enough rpm the suction would actually stick the slide to the bore or suck it open somehow and not want to return. This is downright terrifying. There isn't the same effect with the butterflies of a CV carb so the springs can be softer.

    Yes, you can reduce the spring effort a bit, but it's a dangerous game. Everything will seem fine until you hit the wrong wrist/rev combo. Hopefully nothing else important is going on when you discover that.

    I don't think that it's the rotation stiffness that is fatiguing so much as the constant grip tension required for traction. Stock grips aren't bad in that regard, but slippery gloves are useless. I have a pair that I rub beeswax on regularly just to get enough grip that my arm pressure will hold the throttle without constant squeezing.

    Best of luck.
    '82 GS450T

  10. #10
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    Back in the dim times, before CV carbs became ubiquitous, I’d see an ad in the back of every bike mag for a device called Twist-Assist, or something close to that. Might be worth searching eBay or other vintage bike forums for one.
    Rich Desmond
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