Dynamics of choke cable operation

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roymck
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Dynamics of choke cable operation

Post by roymck » Tue Feb 26, 2019 6:48 pm

The choke cable on my car runs in from the dash and round the engine via the front end of the engine to the carb so I want to neaten the cable run to shorten it and neaten things up .
I am sure I have seen this method of operation on a control cable before . I am sure it works but not quite able to understand how , maybe if we have any keen cyclists out there maybe they have seen it work .
So in the picture 1 and 2 shows how it works at the moment with the outer cable fixed and the inner cable applying the forward and back motion to the operating lever .
Picture 3 and 4 shows the cable direction reversed and the inner cable now fixed and the outer cable applying the push pull movement to the operating lever. This can only work if the outer cable is spiral wound and will stretch .
9BB8B97D-9A92-4379-A2C2-6B16B1AE1359.jpeg
9BB8B97D-9A92-4379-A2C2-6B16B1AE1359.jpeg (135.71 KiB) Viewed 680 times
Any thoughts please , I am sure I am not mad , well not completely.



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Dynamics of choke cable operation

Post by scimjim » Tue Feb 26, 2019 6:54 pm

Nope, the outer is fixed at the knob end so won’t move when you pull or push the inner.


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Dynamics of choke cable operation

Post by roymck » Tue Feb 26, 2019 7:09 pm

scimjim wrote:
Tue Feb 26, 2019 6:54 pm
Nope, the outer is fixed at the knob end so won’t move when you pull or push the inner.
That’s what I thought but I thought maybe be outer cable stretches to make this work.



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Dynamics of choke cable operation

Post by scimjim » Tue Feb 26, 2019 7:14 pm

You’d need a very flexible outer and very rigid inner to make the outer bend to accommodate the extra length (and a good lock) - plus your choke knob will be in for choke and out for normal running.

Can you reverse the lever to hinge at the top, or fashion a bell crank to change the direction of movement?


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Dynamics of choke cable operation

Post by philhoward » Tue Feb 26, 2019 8:29 pm

Fit a carb with an auto choke?

Virtually all control cables work on the same principle (both the inner and outer don’t change length in use). Whether they are push/pull or pull (with a spring return) decides if they have a solid or flexible inner - generally.

What you’ve sketched looks like it won’t work because you’re changing the direction of the travel. It will work if you change it to a solid inner type and accept that you pull the choke out to turn it off and push it in to turn it on.


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Dynamics of choke cable operation

Post by David Tew » Tue Feb 26, 2019 8:33 pm

The same reverse-pull principle is used in cycling as (apparently :? ) it increases the weight of the pull. As I understand it, the outer compresses rather than stretches and the movement relies on there being a curve in the cable so it won't be effective on a straight pull.

Given the caveats above, your suggestion should work and IMHO it will be the same way around i.e. inner shortened at the carb = choke on. However, you'll need a generous, gentle loop of slack to operate so you might not achieve too much. Worth a little experimentation though?

(Oh, and take your camera off the Antipodean setting! :lol: )


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Dynamics of choke cable operation

Post by scimjim » Tue Feb 26, 2019 8:54 pm

David Tew wrote:
Tue Feb 26, 2019 8:33 pm
IMHO it will be the same way around i.e. inner shortened at the carb = choke on.
shortened at the carb means relaxing the outer, which is choke knob pushed in.
David Tew wrote:
Tue Feb 26, 2019 8:33 pm
(Oh, and take your camera off the Antipodean setting! )
unlikely to be the camera, something in the settings (as discussed previously) - my Apple products auto-rotate them.


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Dynamics of choke cable operation

Post by scimjim » Tue Feb 26, 2019 8:56 pm

Is it the right way up now?


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Dynamics of choke cable operation

Post by roymck » Tue Feb 26, 2019 9:02 pm

Well that’s odd as it came out the right way when I view it!



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Dynamics of choke cable operation

Post by philhoward » Tue Feb 26, 2019 9:03 pm

It was the right way up and I still got it wrong.. :oops:


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Dynamics of choke cable operation

Post by David Tew » Tue Feb 26, 2019 9:05 pm

scimjim wrote:
Tue Feb 26, 2019 8:54 pm
shortened at the carb means relaxing the outer, which is choke knob pushed in.
Wouldn't that mean that on a bike with reverse-pull levers you'd need to keep the brake lever pulled to keep the brakes off? :? Any keen cyclists out there?
scimjim wrote:
Tue Feb 26, 2019 8:54 pm
unlikely to be the camera
I was jesting. :)


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