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Old 14th May 2019, 13:14   #1
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Default Engine-Kill switch for Motorcycles

Hey guys,

Finally with some help from fellow enthusiast(Sibun@xBhp) I was able to understand how the ignition switch on motorcycles are wired.

Wiring

Engine-Kill switch for Motorcycles-imag0040.jpg

In total there are 4 wires in the ignition key connector, the thick wires(White & Brown) when when given continuity pass 12V DC current from the battery to the electricals, the skinny wires(Black's) when given continuity would ground the ignition circuit hence killing spark.

Ignition Switch

This has only two positions;

OFF:

Continuity between Ignition Ground Wires.
No-Continuity between 12v DC Wires.

ON:

No-Continuity between Ignition Ground Wires.
Continuity between 12v DC Wires.

Decoding

To find what is what you should get hold of a multimeter and set it to continuity mode, then disconnected the ignition key wiring and on the ignition key connector side, at Key Position OFF see which two wires have continuity, now toggle to Key Position ON the continuity should be disrupted, try a couple of times to be certain.

Bonus Tip:

Now using commonsense you could reverse the above procedure to find the 12v DC line as well. Set multimeter to DC Volts and on harness side of connector connect one multimeter lead and connect the other end to chassis, the 12v DC-IN supply would register 12.x Volts.

Once you have found which color wire supplies 12V DC current, you need to find its combination that takes 12V DC-OUT to the electricals.

For that set multimeter to continuity mode and on the ignition key connector side connect one lead to the same color wire you've found out for 12V DC-IN on harness side earlier. Take the other lead and connect it to other wires and find which combination that has continuity when Key Position ON and continuity disrupts when toggled to Key Position OFF, that wire would be your 12V DC-OUT to the electricals.

Now to connect accessories, you should take (+) supply from 12V DC-OUT to the electricals and for (-) simply ground to chassis.

Now you have accessories line that can be controlled with the ignition key switch.

Wiring

Source a quality switch, I went for the Right-Side Switch-Gear sourced from Royal Enfield that came on old generation Cast Iron Bullets.

Engine-Kill switch for Motorcycles-img20190513wa0044.jpg

Now take the two wires from the switch and connect it to both skinny wires(Black's)

Engine-Kill switch for Motorcycles-imag0043.jpg

Due to lack of space, using a safety pin I popped out the pins, wrapped the switch wires on the naked pins and then re-inserted them into the connector, for a near factory-finish setup without any wires getting spliced.

Here's a video showing everything in action:



Keep and eye on the 'Neutral' light, it stays ON even after the engine has been killed, meaning all electrical's would work, only the engine would remain dead until switch is toggled.

Note to self, use Rubbing Alcohol to erase the symbols on the RE console when OCD sets in.

Cheers,
A.P.

Last edited by ashwinprakas : 14th May 2019 at 13:30.
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Old 14th May 2019, 14:22   #2
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Default re: Engine-Kill switch for Motorcycles

Did I see the switch toggle position is opposed to how it has to be? Cross mark position is supposed to be engine kill IMO.
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Old 14th May 2019, 14:33   #3
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Default re: Engine-Kill switch for Motorcycles

Quote:
Originally Posted by Mr.Boss View Post
Did I see the switch toggle position is opposed to how it has to be? Cross mark position is supposed to be engine kill IMO.
Yeah you did.

Hence why I'd mentioned in the last part about erasing the symbols with Rubbing Alcohol.

Reason for this is because the switch is from a Royal Enfield Cast Iron Bullet(Rs.235/-), on which when continuity is present between wires the motor runs, whereas on the CT100B we've wired it the other way by tapping on to ignition switch, where motor runs only if there isn't continuity between the wires intended to ground ignition.

A switch is just a switch, but the reason I used this is because of crappy quality of aftermarket options.

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These only look good in pictures, in reality the quality is crap and cannot be depended upon, especially when riding in the rain.

Cheers,
A.P.

Last edited by ashwinprakas : 14th May 2019 at 14:34.
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Old 14th May 2019, 15:12   #4
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Default re: Engine-Kill switch for Motorcycles

Informative thread, ashwinprakas! I too contemplated getting a kill switch on my 2015 Honda CB Shine 125, but then figured it's not much of a hassle turning the ignition switch off and on at signals


Quote:
Originally Posted by ashwinprakas View Post
A switch is just a switch, but the reason I used this is because of crappy quality of aftermarket options.

These only look good in pictures, in reality the quality is crap and cannot be depended upon, especially when riding in the rain.
I have two of these on my bike, one for the hazard lights and one for the fog lamps.

They've survived the rains pretty well till now, and even survives the occasional pressure washes. Haven't deteriorated cosmetically either.

Adding a picture of the switches:

Engine-Kill switch for Motorcycles-img20180826wa0007.jpeg

Last edited by boniver : 14th May 2019 at 15:23.
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Old 14th May 2019, 15:46   #5
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Default re: Engine-Kill switch for Motorcycles

Quote:
Originally Posted by boniver View Post
Informative thread, ashwinprakas! I too contemplated getting a kill switch on my 2015 Honda CB Shine 125, but then figured it's not much of a hassle turning the ignition switch off and on at signals
For that I use the choke, as it's conveniently located on old school motorcycles(below horn switch), since it doubles to kill the engine as I recall my dad doing the same on his 2T motorcycle back in the day.

The reason for an engine kill switch is so that the engine stays dead until toggled.

While descending sharp off-road declines, it's sometimes required that you kill the motor and use the clutch as rear brake while tip-toe'ing down.

In such a scenario you cannot go by safely without an engine kill switch, because if I kill the motor using Choke then while descending it will turn back ON once the rear wheel turns, if I turn off ignition then the Horn stops working and I'm at the mercy of jeeps and other motorcycles climbing uphill.

Hence why the Engine Kill switch is of paramount importance when it comes to safety on motorcycle used to frequent off-road terrains.

Quote:
I have two of these on my bike, one for the hazard lights and one for the fog lamps.

They've survived the rains pretty well till now, and even survives the occasional pressure washes. Haven't deteriorated cosmetically either.
I had bought a pair a while ago when I started toying with the idea, but when disassembling one of the switches I simply found the quality to be not up to my standards.

Ignoring the plastic mechanism, the wires were of below par quality, almost like silk threads, would slip when you try to twist them after stripping.

Not something I'd trust with my igntion, wouldn't want things to go south when least expected.
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Old 14th May 2019, 16:13   #6
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Default re: Engine-Kill switch for Motorcycles

Quote:
Originally Posted by ashwinprakas View Post
For that I use the choke, as it's conveniently located on old school motorcycles(below horn switch), since it doubles to kill the engine as I recall my dad doing the same on his 2T motorcycle back in the day.
How is the choke used to kill the engine? Sorry for my query, I've only been riding for two years now, so I'm quite ignorant about some things. As far as I know, the choke is always turned off, and is opened only when the engine refuses to start in the winter. I mean, that's what I've always used it for. So since opening the choke keeps the revs built up, I can't understand how that would kill the engine. Please enlighten


Quote:
While descending sharp off-road declines, it's sometimes required that you kill the motor and use the clutch as rear brake while tip-toe'ing down.
I've obviously never off-roaded much (atleast not as much as you have), but irrespective of whether I'm on the bike or the car, I've never killed the engine on the go since I use engine braking a lot, especially while descending a slope.
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Old 14th May 2019, 17:07   #7
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Default re: Engine-Kill switch for Motorcycles

Quote:
Originally Posted by boniver View Post
How is the choke used to kill the engine? Sorry for my query, I've only been riding for two years now, so I'm quite ignorant about some things. As far as I know, the choke is always turned off, and is opened only when the engine refuses to start in the winter. I mean, that's what I've always used it for. So since opening the choke keeps the revs built up, I can't understand how that would kill the engine. Please enlighten
I thought the same was self explanatory since the thing is called 'Choke' to begin with.

Jokes apart, when you engage choke, it cuts off air-supply to the combustion chamber, meaning when the motorcycle is cold, it helps starting up as this rich'ens(Rich i.e More Fuel) the AFR(Air Fuel Ratio) and ensures that the motorcycle starts effortlessly.

But once warmed up to operating temperatures, if you use Choke the engine simply dies as it has less than adequate Air to burn the fuel that is being fed into the combustion chamber.

Quote:
I've obviously never off-roaded much (atleast not as much as you have), but irrespective of whether I'm on the bike or the car, I've never killed the engine on the go since I use engine braking a lot, especially while descending a slope.
Same here as far as engine braking goes, what I'd mentioned is for the trickier sections, where you cannot afford to use your right foot to brake, using the front brake is clearly not an option due to the type of terrain.

You come to a stop, kill the motor, tip-toe using both feet, using clutch instead of rear brake.

Engine-Kill switch for Motorcycles-clutch.jpg

Source:

This is only for the radical descents where it is even hard to walk downhill, else you're good to go.
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Old 14th May 2019, 18:36   #8
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Default re: Engine-Kill switch for Motorcycles

Wow, now the "Choke" part hits me. Surely, there must've been a reason for them to name it so. Why didn't I think of it before?

Thank you so much for explaining everything so patiently!
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Old 15th May 2019, 16:10   #9
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Default Re: Engine-Kill switch for Motorcycles

Quote:
Originally Posted by ashwinprakas View Post
These only look good in pictures, in reality the quality is crap and cannot be depended upon, especially when riding in the rain.
You are right about this switch, Ive run through two of these switches. Crap for sure.
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Old 16th May 2019, 09:22   #10
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Default Re: Engine-Kill switch for Motorcycles

Quote:
Originally Posted by ashwinprakas View Post
I thought the same was self explanatory since the thing is called 'Choke' to begin with.

Jokes apart, when you engage choke, it cuts off air-supply to the combustion chamber, meaning when the motorcycle is cold, it helps starting up as this rich'ens(Rich i.e More Fuel) the AFR(Air Fuel Ratio) and ensures that the motorcycle starts effortlessly.

But once warmed up to operating temperatures, if you use Choke the engine simply dies as it has less than adequate Air to burn the fuel that is being fed into the combustion chamber.
On modern bikes choke is not what a choke does.

The word originated because it was a device designed to cut off the air supply and thus enrich the mixture to help start the engine.

But the choke on almost all modern (say 80s and up) carburetors found on bikes sold does not have a "Choke". Instead they have an enricher circuit to let in more fuel when choke is applied.

2 wheeler carburetors i have worked on are Mikuni/Mikarb VM, Mikuni TM, Mikuni CV, Keihin flatslide, Dellorto PHBH, and Chetak's Spaco none of these had an air choking device, choke on all of them were enricher circuits.

So pulling choke to cut off the engine will let in more fuel (flood the engine) which will put the flame out and thus kill the engine. It is not realy recommended to do this because it will foul the spark plugs.
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Old 16th May 2019, 13:11   #11
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Default Re: Engine-Kill switch for Motorcycles

Quote:
Originally Posted by Sankar View Post
On modern bikes choke is not what a choke does.

The word originated because it was a device designed to cut off the air supply and thus enrich the mixture to help start the engine.

But the choke on almost all modern (say 80s and up) carburetors found on bikes sold does not have a "Choke". Instead they have an enricher circuit to let in more fuel when choke is applied.

2 wheeler carburetors i have worked on are Mikuni/Mikarb VM, Mikuni TM, Mikuni CV, Keihin flatslide, Dellorto PHBH, and Chetak's Spaco none of these had an air choking device, choke on all of them were enricher circuits.
I guess you've not worked on a PB style Keihin, because from the date of their first arrival in India in the 1980's(I guess) to their latest iteration in 2019 that comes with a TPS, they still sport a Choke Plate.

Engine-Kill switch for Motorcycles-img20190516wa0004.jpg

Engine-Kill switch for Motorcycles-img20190516wa0005.jpg

The above picture is from a friends motorcycle, my CT100B uses the same carburetor i.e Keihin PB16, and has a cable actuated Choke at the handle bar which is connected to a similar butterfly plate, but only spring loaded rather than the stopper type seen in the picture.

The PB's are similar to the VM's which use an enricher but aren't used on current commuters.

Quote:
So pulling choke to cut off the engine will let in more fuel (flood the engine) which will put the flame out and thus kill the engine. It is not realy recommended to do this because it will foul the spark plugs.
Even in the case of an enricher circuit, when you kill the motor by engaging it you're not flooding the motor, you're still choking it as the rev's drop once the AFR rich'ens, if it doesn't then that's a different issue we know too well about.

Guess the differentiation is similar to that between Strangulation and Drowning, basically you don't get enough air to function and die.

Back to point, basically you can't flood the motor when killing it with the Choke, you can only flood it when trying to start it with the choke.

I say this because I've had my ZMA for close to 60k km's before selling it and from day one I'd kill it with the choke due to lack of a kill-switch, and the thing never flooded on the stock carburetor(CVK30), only time it flooded was when running on a VM28 as I'd failed to check spark(motorcycle was left idle for months) before trying to start it with the choke.

Regards,
A.P.

Last edited by ashwinprakas : 16th May 2019 at 13:31.
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Old 16th May 2019, 14:36   #12
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Default Re: Engine-Kill switch for Motorcycles

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Originally Posted by ashwinprakas View Post
I guess you've not worked on a PB style Keihin, because from the date of their first arrival in India in the 1980's(I guess) to their latest iteration in 2019 that comes with a TPS, they still sport a Choke Plate.
No, the first Keihin i had was an aftermarket D slide (not flat) which I put on the RX 5 speed, it had enricher. Karizma's Keihin had enricher iirc, that was later replaced with a Mikuni TM.

Quote:
Guess the differentiation is similar to that between Strangulation and Drowning, basically you don't get enough air to function and die.
The difference is in the post mortem, in one case lungs would be dry and in the other lungs would be wet.

There is a difference in how the engine dies between these two methods, flooding and choking. If there is a choke plate then its ok. If its an enricher its not correct. Excess fuel inside engine is not a good idea, especially when used to kill the engine.
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Old 17th May 2019, 00:34   #13
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Default Re: Engine-Kill switch for Motorcycles

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Originally Posted by ashwinprakas View Post
Jokes apart, when you engage choke, it cuts off air-supply to the combustion chamber, meaning when the motorcycle is cold, it helps starting up as this rich'ens(Rich i.e More Fuel) the AFR(Air Fuel Ratio) and ensures that the motorcycle starts effortlessly.

But once warmed up to operating temperatures, if you use Choke the engine simply dies as it has less than adequate Air to burn the fuel that is being fed into the combustion chamber.
Wow, using choke to kill an engine is new to me. Is the choke mechanism different for 2 wheeler engines? Because in our 99 carburetor Omni, pulling the choke means rise in idling RPM. Even with a warmed up engine, pulling the choke means the engine RPM would increase.

I do know that pulling the choke, chokes the engine of air & hence it runs on a richer fuel-air mixture. But never thought that it could choke the engine (of a 2 wheeler) so much, that it would die .

P.S- Our 99 Omni has a single barrel Mikuni carburetor.

Last edited by chiranjitp : 17th May 2019 at 00:41.
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Old 17th May 2019, 01:36   #14
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Default Re: Engine-Kill switch for Motorcycles

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Originally Posted by chiranjitp View Post
Wow, using choke to kill an engine is new to me. Is the choke mechanism different for 2 wheeler engines? Because in our 99 carburetor Omni, pulling the choke means rise in idling RPM. Even with a warmed up engine, pulling the choke means the engine RPM would increase.

I do know that pulling the choke, chokes the engine of air & hence it runs on a richer fuel-air mixture. But never thought that it could choke the engine (of a 2 wheeler) so much, that it would die .

P.S- Our 99 Omni has a single barrel Mikuni carburetor.
I have no clue about Car Carburetors, but going by logic they should run similar to the Carburetors found on motorcycles, since it is a device that facilitates carburetion, and as for choke there are only two types, Choke Plates and Enrichers.

Though it might seem that I've been using the Choke to kill the motor just like my dad has been doing, there's more to it.

Say when I pull the choke and the motorcycle fails to die and rather starts to rev-up I immediately know that there's an air leak and change my intake manifold and O-Rings which usually solves the issue.

Because on a warmed up engine, for the revs to climb when choke is applied the AFR should be so Lean that introducing fuel or reducing air makes the motor run better, which is not ideal.

The use of choke should be done with care because other than the inconvenience of the motor flooding(crank at WOT, air being less dense rushes into the combustion chamber and helps ignite the excess fuel present) another concern is 'Bore Wash' a phenomenon that can mess up your cylinder in a matter of km's, have seen this happen to a couple of enthusiasts.

Basically petrol is abrasive in nature and tends to wash out the oil film in the cylinder when present in excess, which results in more friction between the rings and the cylinder, which results in premature wear and tear.

Yet the reason why I still use the Choke is because from experience, you literally cannot flood/bore-wash the motor when killing the engine with the choke, as on a properly tuned machine a warm motor dies the moment you pull the choke, because a Rich AFR drops revs like a brick falling to the ground.

Running with the choke engaged, or turning the motor way too many times without the engine firing is a different case which is a know recipie for bad things to happen.

Hope that clears it,
Cheers,
A.P.
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