Stop Buttons- are they the best way?

Slogger · Feb 26, 2015

Hey gang-
I'm an electronic tech by trade, I build automation control systems for industry. Anyway, after giving our stop buttons the hard stare for a while I figured out why I never liked em.
When you press the button, the blue wire (hot) is momentarily connected to the black (ground) wire, diverting the generated pulses from the coil that feed the CDI. The CDI stops sparking, and the engine stops.
This shouldn't do any harm to the CDI, but what is happening at the magneto coil?
The current spikes through the coil windings until the engine stops turning.
(Zero resistance=infinite current flow) This overload of current, applied repeatedly, might be one reason why the coils fail more often than the CDIs. The windings are of hair-fine wire.
Anyway, I have never liked using it. I tried it once or twice for function, but that's it. Besides, you can stop the engine just by letting the clutch out a bit when idling.

What do ya'll think, does this make sense?
.wee.

Enjoy the Ride!

Southgate Jonny · Feb 26, 2015

I use my choke lever (nt carb). Stops the engine instantly.

2door · Feb 26, 2015

The kill switch isn't just for convenience. It is a safety feature. In the event of a stuck throttle or any need to shut down the engine quickly it is the only way. You can't rely on reaching down to fumble with a choke lever and letting the clutch out won't do anything if you're at speed. Every motor vehicle I've ever seen had some way to shut the engine down quickly. Our bikes need them too.

As for damaging the magneto coil. I have to doubt that. I've been around for a while, built and ridden my share of bikes and have yet to have a mag coil failure that could be attributed to using the kill switch. Broken wires, maybe, but not burned which would be the result if your theory was correct. Simply shunting the current to ground should have no ill effects on the coil.

I understand your reasoning but it isn't correct when applied to the magneto.

Tom

Southgate Jonny · Feb 26, 2015

Good point, Tom. I should have clarified that pulling up the choke lever is how I shut my engine down in a NON-EMERGENCY situation.

Slogger · Feb 26, 2015

2door said:
The kill switch isn't just for convenience. It is a safety feature. In the event of a stuck throttle or any need to shut down the engine quickly it is the only way. You can't rely on reaching down to fumble with a choke lever and letting the clutch out won't do anything if you're at speed. Every motor vehicle I've ever seen had some way to shut the engine down quickly. Our bikes need them too.

As for damaging the magneto coil. I have to doubt that. I've been around for a while, built and ridden my share of bikes and have yet to have a mag coil failure that could be attributed to using the kill switch. Broken wires, maybe, but not burned which would be the result if your theory was correct. Simply shunting the current to ground should have no ill effects on the coil.

I understand your reasoning but it isn't correct when applied to the magneto.

Tom

I dunno Tom, if that tiny wire gets hot enough to melt the varnish it would indeed short together. And the spinning magnet continues to induce a current with no current limitation from the load of the CDI as the motor spins down. Think about plug chop tests- high rpm, then short out the coil... which I did myself without any harm. Can't be good for it.

I keep mine but almost never use it.

HDCowboy · Feb 26, 2015

Being an electrician I thought that the way our bikes were wired was a little strange myself. Seems the proper way would have been to use a normally closed switch which would break the hot wire going to the coil to kill the engine when the kill button was pushed. Seems like it would be a pretty easy modification.

2door · Feb 26, 2015

HDCowboy said:
Being an electrician I thought that the way our bikes were wired was a little strange myself. Seems the proper way would have been to use a normally closed switch which would break the hot wire going to the coil to kill the engine when the kill button was pushed. Seems like it would be a pretty easy modification.

It would be easy. Just replace the kill switch with a normally closed switch and wire it in series with the blue wire. I don't see any advantage but it would be simple enough if you're that concerned with magneto coil damage.

Tom

Mike B · Feb 26, 2015

Slogger said:
Hey gang-
I'm an electronic tech by trade, I build automation control systems for industry. Anyway, after giving our stop buttons the hard stare for a while I figured out why I never liked em.
When you press the button, the blue wire (hot) is momentarily connected to the black (ground) wire, diverting the generated pulses from the coil that feed the CDI. The CDI stops sparking, and the engine stops.
This shouldn't do any harm to the CDI, but what is happening at the magneto coil?
The current spikes through the coil windings until the engine stops turning.
(Zero resistance=infinite current flow) This overload of current, applied repeatedly, might be one reason why the coils fail more often than the CDIs. The windings are of hair-fine wire.
Anyway, I have never liked using it. I tried it once or twice for function, but that's it. Besides, you can stop the engine just by letting the clutch out a bit when idling.

What do ya'll think, does this make sense?

Enjoy the Ride!

Of course it does. That's why I used the white wire to the kill switch. You short that to ground and it's heavier wire and it kills the flux in the core and the motor stops. Not to mention that you also don't have your precious HV CDI input on the 10 cent kill switch.

Slogger · Feb 26, 2015

Mike B said:
Of course it does. That's why I used the white wire to the kill switch. You short that to ground and it's heavier wire and it kills the flux in the core and the motor stops. Not to mention that you also don't have your precious HV CDI input on the 10 cent kill switch.

hey How 'bout that? That's interesting, Mike. I'd have never thought to try it.
The white wire (for optional lighting I think) might be a shorter coil on the same core- sharing the ground but isolated from the main, or is it a tap off the main?
I've read that overloading that wire with too much lighting can make the engine quit. If that's true, it would mean that it is a tap-off.

I'd need to have one here (instead of out there on the arctic tundra) to mess with and see. If it's just a tap, it could possibly doink up the coil.

Actually I think the regular set up is fine, I've used mine without harm. It probably doesn't generate enough juice to burn itself up. It would all depend on its output at zero resistance (shorted).
I just like to kick around ideas to better understand how things work. Maybe even stumble onto an improvement, something that makes our bikes a little more reliable.

TakeiT · Feb 26, 2015

Every small engine shuts off this way. Your lawnmower, dirt bike, weed wacker, whatever. What's happening is the magneto sends a positive current to the spark plug, which is basically a diode. The spark plug is connected to ground, completing the circut which in turn causes it to spark. By pressing the button, you are bypassing the spark plug and going straight to ground, so the power isn't reaching the plug, killing the power. I personally use a key switch, just because.

Popping the clutch to kill the motor is horrible for it. You will just burn out your clutch, its not designed to do that. Its the same reason why new drivers of a manual transmission car tend to burn their clutches quicker (That and riding it), so I wouldn't recommend it. As for using the choke, you're flooding out your engine by doing that, which also isn't good because all you're doing is cutting off the airflow, sending more gas into the cylinder and smothering your spark, which in turn will cause issues on its own as well.

Just use the kill switch, its the safest way for your engine, and its how all engines are wired. The magneto is designed to be grounded out.

GoreWound · Feb 26, 2015

I am not really well versed in electrical things, but wouldn't putting a small resistor on the ground line coming off the kill switch protect against this issue?

also if you wired it by grounding to the frame would the whole bike not become a giant resistor?

Slogger · Feb 27, 2015

GoreWound said:
I am not really well versed in electrical things, but wouldn't putting a small resistor on the ground line coming off the kill switch protect against this issue?

also if you wired it by grounding to the frame would the whole bike not become a giant resistor?

It's not a big issue, they work as is. A resistor might keep the kill switch from stopping the motor, if it were too big.
Back to the button-
My engine makes zero torque at idle, I ease the clutch out a bit and it stops without the slightest drama. My clutch is tougher than some, I guess.
If I crashed and gas was leaking all over while the engine is screaming away, I would hit the kill button.

This forum has lots of threads where people are told the mag coils are a main failure part, there are even riders carrying spares in toolkits on the bikes, according to what they have said on here.
I have read that the tiniest bit of water can make them go out, that new bikes run fine for a couple hours then they go out, in other words, they go out quite a bit.
Maybe the good old kill button is a factor.
That's all I was trying to put out there.
BTW, my lawn machine mower uses a brake on the rotor to stop the engine.
I think I'll let this one end here.

Happy Trails!
drn2

scotto- · Feb 27, 2015

As I was having some issues at the end of last year with my kill switches acting up at the races, I disconnected both of them and the problem seemed to go away. The ignition system seemed to be grounding out for some strange reason and disconnecting the kill switches alleviated that problem.

To kill the 212+cc monster I just put my hand on the end of the Uni foam filter and collapse it to the rear of the mikuni carburetor (cutting off the air source) and blipping the throttle. That's a mechanical way of choking an engine.....

GoreWound · Feb 27, 2015

an ideal set up would kill the air, gas, and spark.
but I do not think it is truly possible to cut gas flow on a float carb, at least not immediately.

instead of letting out the clutch when stopped to kill it maybe slowing down and stopping gradually without disengaging the engine would be less wear and tear. when I first got mine running i accidentally stopped the engine with the clutch and the process did not leave me with a sense of confidence in making a habit of it. but each motor is unique, maybe mine just is noisy about doing that and yours is okay with it.

likewise not all engines will show any magneto coil issues, this sort of issue may not come up for many, but I'd bet someone out there read this post and had a eureka moment.

judging from what I have seen I'd bet maybe a third of coils that fail due to 'water somehow' were probably going to fail anyway due to bad quality control.

short of building your own magneto coils I don't think that issue can be solved too easily.

frankly my motor impresses me with how well it runs on such low quality parts. soon I'm going to get my new carb onto it, and swap out the plug and boot for normal ones, and I can't wait to see how it runs.

I was about to hit post when I thought of something: has anyone out there with a compression release used it when stopping their motor? what is that like?

mapbike · Feb 27, 2015

just reach down and pull spark plug boot off the plug, but be sure you have securely strattled the top bar or fuel tank on the bike, not hard enough it hurts but firm enough to know your sorta sitting on the top bar before you touch the plug wire, everything shuts down much better this way.

scotto- · Feb 27, 2015

GoreWound said:
I am not really well versed in electrical things, but wouldn't putting a small resistor on the ground line coming off the kill switch protect against this issue?

also if you wired it by grounding to the frame would the whole bike not become a giant resistor?

Kill buttons/switches normally ground to the frame (or handlebars at least).....I call it ground but you could call it a huge resistor if you like......

Intrepid Wheelwoman · Feb 27, 2015

My VeloSolex stops just fine on the compression release and various other old motorcycles I've owned with compression releases did the same. Some Villiers engines had a springy brass tab on the cylinder head which was pushed down to make contact with the top of the spark plug when you wanted to stop the engine. Nice and simple and it works every time.

cannonball2 · Feb 27, 2015

I use the old tried and true grounding clip at the spark plug. Not only does it negate the rather untidy wiring, its grounding the circuit at the end. It is short circuiting the spark plug sending the CDIs output to ground which its just as happy doing as sparking the plug. The ultimate in simplicity. Mine is the locking type, you DO have to remember to return it to its unlocked position. No fun reaching down while pedal starting to unlock it and grabbing the wire when it breaks contact!

mapbike · Feb 27, 2015

cannonball2 said:
I use the old tried and true grounding clip at the spark plug. Not only does it negate the rather untidy wiring, its grounding the circuit at the end. It is short circuiting the spark plug sending the CDIs output to ground which its just as happy doing as sparking the plug. The ultimate in simplicity. Mine is the locking type, you DO have to remember to return it to its unlocked position. No fun reaching down while pedal starting to unlock it and grabbing the wire when it breaks contact!

Well I guess you beat me to it, I was gonna suggest the old lever on the head myself, work for many years just fine on the lawn and garden equipment, simple, easy and nothing to even go out with it.

Works like a champ.

MEASURE TWICE · Mar 1, 2015

I never had a problem with a magneto going out on many of Briggs engines that are old and have quite a bit of use. They are from the 80's era and other things needed replacement, but not the magneto. I never had water cause a problem with a magneto either with the Briggs. Once the epoxy potting over the magneto had given me a bit of trouble only since the low tension solid wire was cracked off right at the epoxy. I used an old solder pencil tip and melted just enough of the epoxy to get to the wire and soldered and RTV potted a high temp very flexible stranded wire for the broken off one.

I have only a year ago got a junked CG engine type Coleman Generator that had a bad magneto. I basically use re-purposed old engines so the experience otherwise was with Clinton and Tecumseh engines which are a novelty I guess now.

Engine stopping with a brake (lawn mower blade) as for mandated by government, also uses kill switch as well from what I know.

The very old coils an maybe magnetos too, sometimes I hear have to be activated again some way I am not all too familiar with. Physically they are OK, but a small magnetism or something must be remaining within the coil/lamination or something. This is also the case for the generator winding not found on most motor bikes. The process is called flashing the coil and are separate from recharging the magnet on the flywheel.

Stop Buttons- are they the best way?

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