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Old 04-29-2014, 04:47 AM   #16
snarf
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You guys are mistaken if you think the push cable will be able to overpower the pull cable, in the event of a cable jamming up. That's not what it was designed for.

Ever ridden a 500 two stroke? The can surge on you when you chop the throttle shut. Surging is when the piston's pulling so much vacuum that it causes the slide to 'jump' [there's more to it than this, but its the basic idea] a little- and that causes the bike to give you a little extra boost- even if you didn't ask for it :)

The push/pull throttle is something made up to try and sidestep this, because big thumpers create a lot of vacuum, too.

Usually, the push/pull cables are NOT the same, so the idea of having it as a spare, while a good idea on paper, wont do anything for you in the real world.

Some of my 450s I've removed the push cable, some not. I like pulling the push cable,a s it makes the throttle lighter overall, and there's less parts to fail.

YMMV.
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Old 04-29-2014, 06:51 AM   #17
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Quote:
Originally Posted by snarf View Post
You guys are mistaken if you think the push cable will be able to overpower the pull cable, in the event of a cable jamming up. That's not what it was designed for.

Ever ridden a 500 two stroke? The can surge on you when you chop the throttle shut. Surging is when the piston's pulling so much vacuum that it causes the slide to 'jump' [there's more to it than this, but its the basic idea] a little- and that causes the bike to give you a little extra boost- even if you didn't ask for it :)

The push/pull throttle is something made up to try and sidestep this, because big thumpers create a lot of vacuum, too.

Usually, the push/pull cables are NOT the same, so the idea of having it as a spare, while a good idea on paper, wont do anything for you in the real world.

Some of my 450s I've removed the push cable, some not. I like pulling the push cable,a s it makes the throttle lighter overall, and there's less parts to fail.

YMMV.
Virtually all modern motorcycles prior to FI use a CV type carburetor and a push/pull cable system. In a CV carburetor there is no physical connection whatsoever between the slide and the opening/closing throttle cables, none, zero. The cables attach to and control the opening/closing of the butterfly valve. The slide is not physically connected to the cables in any way and is designed to move completely freely and independent in response to changes in manifold vacuum.

The push/pull cable system is there solely to provide positive control over the opening/closing of the butterfly valve in the event the return spring is unable to close it (return spring failure or sticky pull cable). Properly routed and lubricated push/pull cables should have little friction. Most of the tension felt at the throttle is due to the return spring and throttle body or butterfly springs, so removing the second cable on a properly working system should result in virtually no describable change to the weight or action at the throttle grip.

JohnCW screwed with this post 04-29-2014 at 07:04 AM
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Old 04-29-2014, 07:41 AM   #18
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Originally Posted by snarf View Post
You guys are mistaken if you think the push cable will be able to overpower the pull cable, in the event of a cable jamming up. That's not what it was designed for.

Ever ridden a 500 two stroke? The can surge on you when you chop the throttle shut. Surging is when the piston's pulling so much vacuum that it causes the slide to 'jump' [there's more to it than this, but its the basic idea] a little- and that causes the bike to give you a little extra boost- even if you didn't ask for it :)

The push/pull throttle is something made up to try and sidestep this, because big thumpers create a lot of vacuum, too.

Usually, the push/pull cables are NOT the same, so the idea of having it as a spare, while a good idea on paper, wont do anything for you in the real world.

Some of my 450s I've removed the push cable, some not. I like pulling the push cable,a s it makes the throttle lighter overall, and there's less parts to fail.

YMMV.
My KTM 640 ADV with CV carb and my Vstrom 640 with fuel injection both have pull to close cables.
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Old 04-29-2014, 08:01 AM   #19
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My KTM 640 ADV with CV carb and my Vstrom 640 with fuel injection both have pull to close cables.
This. There's NO "push" involved. Pull to open, pull to close.
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Old 04-29-2014, 08:02 AM   #20
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Quote:
Originally Posted by JohnCW View Post
Virtually all modern motorcycles prior to FI use a CV type carburetor and a push/pull cable system.
Err.. virtually all? lol.

Quote:
Originally Posted by JohnCW View Post
The push/pull cable system is there solely to provide positive control over the ope ... snip ...
Seriously dude, did you even read my post before you copy/pasted out of your clymers?

I'm not talking about EPA and federally regulated throttle bodies, or CV [vacuum slide] carbs. I love how as soon as someone with real world experience posts up, the peanut gallery chimes in.
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Old 04-29-2014, 08:09 AM   #21
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Originally Posted by snarf View Post
Err.. virtually all? lol.



Seriously dude, did you even read my post before you copy/pasted out of your clymers?

I'm not talking about EPA and federally regulated throttle bodies, or CV [vacuum slide] carbs. I love how as soon as someone with real world experience posts up, the peanut gallery chimes in.
Sorry I posted my real world experience.
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Old 04-29-2014, 08:19 AM   #22
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Originally Posted by snarf View Post
Err.. virtually all? lol.



Seriously dude, did you even read my post before you copy/pasted out of your clymers?

I'm not talking about EPA and federally regulated throttle bodies, or CV [vacuum slide] carbs. I love how as soon as someone with real world experience posts up, the peanut gallery chimes in.
Yes, the vast majority of bikes over the past 20 years have used CV type carbies with twin cable systems. And yes I read your post where you clearly stated the dual cable system was neither designed or would be effective to force the carby shut, but was rather designed to stop "Surging is when the piston's pulling so much vacuum that it causes the slide to 'jump' and the push/pull throttle is something made up to try and sidestep this" You're exact words.

No need to cut & past from a clymers as 40+ years experience as a professional mechanic is enough to know your wrong. Like to share your "real world experience" ....dude?
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Old 04-29-2014, 08:33 AM   #23
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Originally Posted by JohnCW View Post
Yes, the vast majority of bikes over the past 20 years have used CV type carbies with twin cable systems. And yes I read your post where you clearly stated the dual cable system was neither designed or would be effective to force the carby shut, but was rather designed to stop "Surging is when the piston's pulling so much vacuum that it causes the slide to 'jump' and the push/pull throttle is something made up to try and sidestep this" You're exact words.

No need to cut & past from a clymers as 40+ years experience as a professional mechanic is enough to know your wrong. Like to share your "real world experience" ....dude?
Sounds like he's still living in the land of dirt bike carburetors, Mikuni VMs and such, that CAN'T use a 2 cable setup.
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Old 04-29-2014, 09:24 AM   #24
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Originally Posted by JohnCW View Post
Yes, the vast majority of bikes over the past 20 years have used CV type carbies with twin cable systems. And yes I read your post where you clearly stated the dual cable system was neither designed or would be effective to force the carby shut, but was rather designed to stop "Surging is when the piston's pulling so much vacuum that it causes the slide to 'jump' and the push/pull throttle is something made up to try and sidestep this" You're exact words.

No need to cut & past from a clymers as 40+ years experience as a professional mechanic is enough to know your wrong. Like to share your "real world experience" ....dude?


I've ridden many open class 2 strokes and never experienced this "surge" he's talking about.

BTW "vacuum" no matter what is pulling on it can never get over about 32" mercury (depending on the atmospheric pressure of the day) so I don't think it matters what engine the carb is attached to, once the pressure drops to 0 (actual pressure, not gauge) "vacuum" is done.
If your 500 2 stroke surges when you close the throttle, you probably have a vacuum leak and are jetted a little rich to compensate.
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Old 04-29-2014, 11:51 AM   #25
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Originally Posted by ttpete View Post
Sounds like he's still living in the land of dirt bike carburetors, Mikuni VMs and such, that CAN'T use a 2 cable setup.
I happen to like that world :) Toss a PWK or a FCR on somethin' and I'm happy :)
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Old 04-29-2014, 03:21 PM   #26
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I happen to like that world :) Toss a PWK or a FCR on somethin' and I'm happy :)
Mikuni does make a flat slide pumper that can use a 2 cable setup and works real well on 4 stroke big singles. HSR42 and 45.
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Old 04-29-2014, 05:25 PM   #27
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Here's my opinion in a little more detail of why the designer's use a twin cable system. Basically it's to achieve a light throttle. This is particularity an issue on an I4 with 5 springs, the main return spring and 4 small coil types at each of the butterfly valve shafts. If they fitted the weight of springs that would essentially guarantee the carbies or throttle bodies would shut all the time you'd end up with an unacceptably heavy throttle. So they fit light springs that will do the job when everything is working perfectly. To cover the event that the throttle may not close due to lack of maintenance etc they fit the second close cable that should add no weigh to the throttle if working properly as a fall back safety solution.

So IMO, the reason for a dual cable throttle system is to safely have as light a throttle as possible. If you remove the second cable you negate this design safety feature, and save what $15? You can then go buy a Big Mac and Coke with the money.
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Old 04-29-2014, 07:38 PM   #28
Anonawesome
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I've ridden many open class 2 strokes and never experienced this "surge" he's talking about.
It's there. Anyone with a dr350 who's fitted a TM33 flat side (not CV) will tell you it'll do it. It's not bad, just at high speeds, WOT, then quickly closing, it'll lurch. Using both cables doesn't help. The cables are also not interchangeable unfortunately, so you can't really keep it as a spare. I recommend buying an actual spare, then zip-tieing it along the length of the original, along with a clutch, and decomp if you have it.

I'm running one cable. The TM33 has a heavy spring and large pulley and is well built. In the (ridiculously unlikely) event that the cable snaps, cutting power will be a safer option than using the other cable to bring it back down to a position that will still leave the engine running.

The spring is not going to snap.
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Old 04-29-2014, 08:44 PM   #29
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In the (ridiculously unlikely) event that the cable snaps, cutting power will be a safer option than using the other cable to bring it back down to a position that will still leave the engine running.

The spring is not going to snap.
I wouldn't describe the likelihood of an accelerator cable breaking as "ridiculously unlikely". It's a bit more common than that. But anyhow if the cable breaks the carby will just close shut.

Ask anyone old enough to have regularly ridden old English bikes with Amal carburetors about sticking throttles if you think this discussion is purely academic or the manufacturer decided to over engineer the bike for no purpose whatsoever. Google "Amal slide sticking" and you'll be able to entertain yourself for the next week reading the hundreds of pages of posts on the subject.
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Old 04-30-2014, 02:57 AM   #30
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Originally Posted by JohnCW View Post
I wouldn't describe the likelihood of an accelerator cable breaking as "ridiculously unlikely". It's a bit more common than that. But anyhow if the cable breaks the carby will just close shut.

Ask anyone old enough to have regularly ridden old English bikes with Amal carburetors about sticking throttles if you think this discussion is purely academic or the manufacturer decided to over engineer the bike for no purpose whatsoever. Google "Amal slide sticking" and you'll be able to entertain yourself for the next week reading the hundreds of pages of posts on the subject.
I think this is part of the reason for the development of cv carbs.


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