Kill switch for small engine

[bigone5500]

I am going to assume I can use just any N.O. momentary switch for this application. However, I don't know for sure. I have a 6.5HP harbor freight predator motor that I have installed on a gokart. I want to add a kill switch to the kart to stop the motor before getting off for safety. What specs do I need to watch to know if it will work? I know I am grounding the coil and it produces a large amount of voltage but it is not high current...although the current is enough to make one say some high dollar words.

 

[Gryd3]

My motorcycle uses a toggle switch instead of a button.
Hit the switch and the engine dies. (Large rocker toggle on the right hand side of the handle bar.
In fact, I'm sure you could retro fit almost any motorcycle kill switch.

 

[bigone5500]

I also have some toggles. I figure a single wire in series to ground from the on/off switch will suffice.

You know...in saying that, the on/off switch is probably as good as any I have. Another example of answering one's own questions.

Thanks Gryd3.

 

[Gryd3]

I also have some toggles. I figure a single wire in series to ground from the on/off switch will suffice.

You know...in saying that, the on/off switch is probably as good as any I have. Another example of answering one's own questions.

Thanks Gryd3.

Only thing to consider if you are using that on the spark-plug line is that it's rated for the voltage, or the new sparkgap could be inside the switch instead of the motor
Have fun with your toy! I know I have fun with my bike

 

[bigone5500]

Thanks. I have already rode it and know that 6.5hp is way too much for a kart this size. I'm pretty sure it will go 30 MPH. I have adjusted the throttle limit screw to slow it down. Maybe I will finish it by summer.

 

[swagguy8]

For my boat, the kill switch that i installed grounds the positive end of the spark plug leads. i got lazy and didn't use a relay, since any large-resistance wire is always less resistance than the infinite resistance spark plug. It works really well. For the kill switch you could install a flap for the carburetor that blocks the oxygen 100%. I know that many hot rods ECUS/ignition controllers use the method of grounding the spark plug. good luck on your project!

 

[bigone5500]

I will try this out today and update with my findings. It will be after I visit my local going out of business radio shack.

 

[Y2KEDDIE]

I question the technique of grounding the spark plug, although this method has been used since day one with magnetos to modern day small engines.
I recently worked on a electronic capacitive discharge system. It has a stator coils; as the magnetic rotor rotates it generates a voltage which charges a capacitor, the rotor also rotates past hall effect switches which controls the firing order.

The output is 300 V into the primary side of the ignition coil.

This unit relies on grounding this 300V line to stop. I think this puts an excessive stress on the output. A common failure is shorted stator coils from this overload.

I would think the same would apply to small engine ignition. It would be better to to disconnect or add high resitance to the priary side of the ignition winding.

Any thoughts or comments?

 

[bigone5500]

I do remember in old tillers, the engine was turned off by flipping a metal toggle, so to speak, over to the spark plug which grounded the coil to the metal case. I would think this is the same method.