Carb Sinch Shorting Method Advise Needed

[mimmo66]

I've been back from a Tech Day without having learned/experienced the carb shorting method I went there for because nobody uses it.

Everybody seemed to be using some kind of gadget, twinmax and the like, while I just wanted to learn doing it the airhead way.

Is it possible to connect a wire with a switch from the plug extension lead to the head via some clips so that instead of using a screwdriver to shorten the spark plug I would just flick the switch on/off.

Thank you for any advise,

Domenico

[Barry]

Is it possible to connect a wire with a switch from the plug extension lead to the head via some clips so that instead of using a screwdriver to shorten the spark plug I would just flick the switch on/off.

In principle yes.  Bear in mind your going to need a switch rated for the high voltages involved which in practice will mean one with large contact gaps say at least 10mm otherwise the spark will prefer to arc across your switch contacts rather than the spark plug gap. Not sure where your going to find such a switch as real HV switches are very very expensive. You might be able to make something though, I seem to remember seeing a home made switch box on one of the Airhead forums so you might find something with a search.

[Ed Miller]

I think you could probably do something like you suggest, but it would be more complicated rather than "simple by choice."  You would need to make one for each side, since the general idea of shorting the spark is to tune the bike so that it sounds the same with either cylinder running by itself which requires being able to move back and forth pretty quickly.

I think most of us on this forum that don't have Twinmax type tools use the $4 carb synchronizer, using tubing and a stick of some kind to make a comparative manometer.  Somebody wrote the details up a while back.  I have a pair of the modified spokes to use the shorting method, but I've only done it on somebody else bike.  

Here's an article on synchronizing carbs.  I read it all, then highlighted and numbered the actual "do this" steps, as they can get lost in the explanatory material.  

http://bmwmotorcycletech.info/synchcarbs.htm

Good luck,

[Yikes]

Dom,

Keep at it with the plug shorters.  I used the shorting method to tune and synch my carbs after the rebuild and it worked great for me.  Just follow Snowbum’s directions (and warnings) in the article that Ed linked to.  I found it very easy to listen and adjust one side and then the other until they sounded the same. It‘s all about matching the rhythm of the firing: 1-2-3, 1-2-3, 1-2-3, 1-2-3 and 1-2-3, 1-2-3, 1-2-3, 1-2-3.  

Here’s a pic of the crude shorters that I made from copper wire and the top bits broken out of 4 old spark plugs.   Remove the wires from the plugs and screw the shorters onto the plugs and connect the wires to the top of the shorters.  Start it up and a screwdriver across the shorter to the head stops that cylinder from firing.  Keep those in your tool kit and you can tweak the tuning anywhere you go anytime that you have the engine warmed up.  

[proctorls]

In principle yes.Bear in mind your going to need a switch rated for the high voltages involved which in practice will mean one with large contact gaps say at least 10mm otherwise the spark will prefer to arc across your switch contacts rather than the spark plug gap.

Barry is exactly right. Unless every component of your wiring AND shorting switch is rated for many kilovolts (read BIG and THICK), you risk a nasty shock or insulation breakdown somewhere you don't want it.  Stick with a solid shorting device that connects directly from the plug terminal to the engine.  Not as easy, but better.

Steve in VT