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Discussion in 'Motorized Bicycle General Discussion' started by jazz2561, May 3, 2015.
Does anyone know how to wire a kill switch to a Briggs and Stratton 5 hp flathead?
These can be wired straight to the sparknplug wire and ground so closing the switch shorts the spark to ground and kills the engine... most older Briggs and Tecumseh engines just had a metal tab with a sharpened spike at the sparkplug and to kill the engine one would just push this tab toward the spark plug piercing the wire cap if it had one and shifting the plug to ground... this was the typical setup on most these engines back in the 70's and early 80's...
Any pictures on this setup?
I don't have any pics since my last Briggs or Tecumseh I did anything with was back in the early 80's... but you may try tootle image searching a Tecumseh 3 or 5hp engine and you'll see the little tab next to the spark plug... to kill the engine just push the tab onto the top of the plug and it shorted out the plug... very simple setup. On the go karts they usually just ran a toggle switch from the frame to the spark plug wire and flipping the switch would kill the engine and prevent it from starting... a normally open push button switch makes things easier because if the toggle switch was in the "on" position the engine would not start... I remember cussing at my go kart after about 10 pulls and no start... then seeing the switch in the wrong position a few times...
http://motorbicycling.com/showthread.php?t=29678&page=19 post 185 on page 19 of my thread
See the condenser has a contact point that has a spring and pushes on a set of wires that one is to the low tension wire to the magneto and the other to the kill switch one side.
Note, the other side of the kill switch is to good ground. When the kill switch is contacted, then it does not matter if the points contact and disconnect as the engine spins, as they are shorted effectively by the kill switch. This is a safer way to stop than the high tension plug wire.
A really good ground would be by using an external star tooth washer and soldered ring terminal to one of the screws through the magneto lamentations where it is used to mount the magneto next to the flywheel.
In any case the handle bars usually have an OK ground, but there is grease between the metal to the neck, so I took a ground from a bracket that is for my jack-shaft on the same platform of the engine. The engine bolts utilize split lock and external star tooth lock washers to hold it in position for a small amount of adjustable tension for a belt drive. The external star tooth lock washers then tie the metal electrically much better.
I also use a wire from that bracket straight to the tightening clamp of the push button kill switch on the handle bars, so I need not worry about the grease affecting a good ground connection. I also parallel a toggle switch that also is a kill switch, but you don't have to hold any button down. Both are there in case the other fails.
I'm on my kindle so posting pics isn't easy but here's a pic of the engine with a kill tab next to the plug... see the little triangle cutouts... those are the spikes to go thru the rubber plug wire cap and short the spark to ground thru this tab....
I fully agree with measure twice's post... the kill tab could sometimes be a shocking experience... supposedly the spark would short out to the engine block but sometimes it would bite you when least expected...