Four stroke double throttle cable necessary?

Hman144
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Hman144
This may be an odd question, but it's been bugging me and not being familiar with modern FI four strokes, I'm coming to those who are.

Why is the double push-pull type throttle cable necessary on four strokes?

I redid an old KLX250 for vintage racing a while back. It had a double cable set up, with an external butterfly valve actuator. It was spring loaded to return to closed. I had a problem one day with the throttle housing, and changed it out with an old single cable set up from a two stroke. Worked just fine.

So why did they need them then, and even more so now with FI?

Thanks in advance for what I'm sure will be a bevy of thoughtful and factual responses.

H
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DynoDan22
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DynoDan22 8/13/2019 10:54am
8/13/2019 10:54am
The double cable setup is more of a safety factor as fourstrokes create so much intake vacuum that theoretically (but rarely if ever happens) the butterfly can stick open by the vacuum. The double cable allows the butterfly to be pulled closed. I have personally run a single cable setup back in the day on a '05 CRF450 but I don't recommend it. It's a safety feature that I'm sure the corporate lawyers mandate for liability.
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Hman144
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Hman144 8/13/2019 11:18am
8/13/2019 11:18am
Ah yes. The Law people.

Not to beat this horse too much, but questions persist.

How can a butterfly valve get "Stuck open" by vacuum at the throat of the carb?

Also, if it's liability issue, why are factory teams running them, what with all that extra weight and all?
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Bennett59
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Bennett59 8/13/2019 3:06pm
8/13/2019 3:06pm
Hman144 wrote:
This may be an odd question, but it's been bugging me and not being familiar with modern FI four strokes, I'm coming to those who are...
This may be an odd question, but it's been bugging me and not being familiar with modern FI four strokes, I'm coming to those who are.

Why is the double push-pull type throttle cable necessary on four strokes?

I redid an old KLX250 for vintage racing a while back. It had a double cable set up, with an external butterfly valve actuator. It was spring loaded to return to closed. I had a problem one day with the throttle housing, and changed it out with an old single cable set up from a two stroke. Worked just fine.

So why did they need them then, and even more so now with FI?

Thanks in advance for what I'm sure will be a bevy of thoughtful and factual responses.

H
Push and pull system. I had a 05 kx250f the return cable broke still could run it just had to manually twist it back up it won’t return on its own.
FWYT
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FWYT 8/15/2019 11:15pm
8/15/2019 11:15pm Edited Date/Time 8/15/2019 11:19pm
Hman144 wrote:
Ah yes. The Law people. Not to beat this horse too much, but questions persist. How can a butterfly valve get "Stuck open" by vacuum at...
Ah yes. The Law people.

Not to beat this horse too much, but questions persist.

How can a butterfly valve get "Stuck open" by vacuum at the throat of the carb?

Also, if it's liability issue, why are factory teams running them, what with all that extra weight and all?
"How can a butterfly valve get "Stuck open" by vacuum at the throat of the carb?"

IN THEORY - the velocity of the intake could overpower the butterfly return spring in WFO.
When it's max airflow and the butterfly is fully in line with said airflow.
Yeah, I don't buy it either.

But yeah, you have double cables on flat slides, too, so I don't know.

The Shop

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Moto Obsessed 8/16/2019 6:05am
8/16/2019 6:05am
My first time rebuilding a carb with push/pull cables was on my '06 SXF250.... Got it all put together, kicked it over and it roared to life at WFO..... I had to roll the throttle forward to bring the revs down and it would snap back if I let go, back to WFO..... I had the cables reversed haha #learningexperience
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omalley
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omalley 8/16/2019 7:42am
8/16/2019 7:42am
Minor note: it’s a pull-pull, not a push-pull.
One cable pulls open, the other pulls closed. The non-pulling cable follows but isn’t pushing.
Shreineken
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Shreineken 10/17/2020 8:40am
10/17/2020 8:40am
Hman144 wrote:
This may be an odd question, but it's been bugging me and not being familiar with modern FI four strokes, I'm coming to those who are...
This may be an odd question, but it's been bugging me and not being familiar with modern FI four strokes, I'm coming to those who are.

Why is the double push-pull type throttle cable necessary on four strokes?

I redid an old KLX250 for vintage racing a while back. It had a double cable set up, with an external butterfly valve actuator. It was spring loaded to return to closed. I had a problem one day with the throttle housing, and changed it out with an old single cable set up from a two stroke. Worked just fine.

So why did they need them then, and even more so now with FI?

Thanks in advance for what I'm sure will be a bevy of thoughtful and factual responses.

H
Question: is the 2nd cable NOT necessary on a 4-stroke Quad? Only on bikes?
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Shreineken
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Shreineken 10/17/2020 8:42am
10/17/2020 8:42am
DynoDan22 wrote:
The double cable setup is more of a safety factor as fourstrokes create so much intake vacuum that theoretically (but rarely if ever happens) the butterfly...
The double cable setup is more of a safety factor as fourstrokes create so much intake vacuum that theoretically (but rarely if ever happens) the butterfly can stick open by the vacuum. The double cable allows the butterfly to be pulled closed. I have personally run a single cable setup back in the day on a '05 CRF450 but I don't recommend it. It's a safety feature that I'm sure the corporate lawyers mandate for liability.
Question: is the 2nd cable NOT necessary on a 4-stroke Quad? Only on bikes?

LKHill
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LKHill 10/17/2020 10:22am
10/17/2020 10:22am Edited Date/Time 10/17/2020 10:24am
Shreineken wrote:
Question: is the 2nd cable NOT necessary on a 4-stroke Quad? Only on bikes?
Evidently not. My TRX 700 don't seem to mind.
sobbinhood
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sobbinhood 9/15/2023 5:30am
9/15/2023 5:30am
Moto Obsessed wrote:
My first time rebuilding a carb with push/pull cables was on my '06 SXF250.... Got it all put together, kicked it over and it roared to...
My first time rebuilding a carb with push/pull cables was on my '06 SXF250.... Got it all put together, kicked it over and it roared to life at WFO..... I had to roll the throttle forward to bring the revs down and it would snap back if I let go, back to WFO..... I had the cables reversed haha #learningexperience

Are the 2 cables generally the same cable? Or are they different? Just picked up an 05 crf and the push or return cable is frayed AF at the throttle housing. I wanted to replace both but most places sell the cables individually and can’t determine if I need 2 of the same cable or what. 

RaceFan
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RaceFan 9/15/2023 6:14am
9/15/2023 6:14am
sobbinhood wrote:
Are the 2 cables generally the same cable? Or are they different? Just picked up an 05 crf and the push or return cable is frayed...

Are the 2 cables generally the same cable? Or are they different? Just picked up an 05 crf and the push or return cable is frayed AF at the throttle housing. I wanted to replace both but most places sell the cables individually and can’t determine if I need 2 of the same cable or what. 

Different cables and should come as a set. One has an adjuster on it and the ends are different to fit into the twist grip throttle housing.

JB500
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JB500 9/18/2023 6:28pm
9/18/2023 6:28pm
Moto Obsessed wrote:
My first time rebuilding a carb with push/pull cables was on my '06 SXF250.... Got it all put together, kicked it over and it roared to...
My first time rebuilding a carb with push/pull cables was on my '06 SXF250.... Got it all put together, kicked it over and it roared to life at WFO..... I had to roll the throttle forward to bring the revs down and it would snap back if I let go, back to WFO..... I had the cables reversed haha #learningexperience

I have nothing to offer this thread, but your comment reminded me years ago I put a new steering box on my then ram 2500. It was geared backwards so when you turned the steering wheel left, the wheels turned right. I was so pissed at first, but my dad and I took it off the lift and drove it around laughing in the parking lot at the shop for a while before going and swapping it out for a different box. 

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