Disconnecting coil?

I have a '71 with Boyer Mk. III. Does it harm anything to disconnect the low-tension side of either coil while the engine is running? I would be doing this when setting the pilot jets and throttle stops. My alternative would be to clamp a dummy spark plug somewhere and jump the high sides to it in turn (NOT while running!).

Thanks.
PS Man, am I glad spring is here!

kartiste said:

I have a '71 with Boyer Mk. III. Does it harm anything to disconnect the low-tension side of either coil while the engine is running? I would be doing this when setting the pilot jets and throttle stops.

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The Boyer ignition (and most other Commando electronic ignitions) works on the wasted spark principal with the coils wired in series, therefore disconnecting a primary circuit wire will stop both coils working, so there will be no sparks at either plug.

Like LAB said...

I remove one plug and reattach it to the coil wire, with a clip lead wire grounding the plug to engine. The motor turns a lot easier with one plug removed.

What would happen if I simply shorted the primary side of a coil?

kartiste said:

What would happen if I simply shorted the primary side of a coil?

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Which side of which coil?

Theoretically there are three options:

1. If you short the primary on the side of the coil which has the Boyer box black wire connection (coil negative,-assuming standard positive earth/ground?) then I think you would lose sparks from both coils.
2. If you short it at either coil's jumper wire connection (the positive terminal on the previously mentioned coil, and negative of the other "second" coil) then I'd expect you'd lose sparks from the second coil?
3. If you short the positive side of the second coil then nothing would happen, as it's the ground wire.

However, doing either of the first two could possibly result in damage to the Boyer box, so personally I wouldn't be inclined to try it-unless our electronics experts here say it's safe to do so?

kartiste said:

I have a '71 with Boyer Mk. III. Does it harm anything to disconnect the low-tension side of either coil while the engine is running? I would be doing this when setting the pilot jets and throttle stops. My alternative would be to clamp a dummy spark plug somewhere and jump the high sides to it in turn (NOT while running!).

Thanks.
PS Man, am I glad spring is here!

Click to expand...

Not really necessary to set up the carbs by disconnecting coil - contrary to the manual. First step - using a drill bit of your choice as a guage, set the throttle stop opening of the two (AMAL) slides at the same open position which is the diameter of the drill bit. 2nd step - start the engine and after warm, set the idle by moving the slide stop screw the same amount on each carb until you get the idle speed desired. 3rd step - start either side, turn in the idle mixture screw until the engine rpm drops making note of how many turns as you open the idle screw until the engine rpm drops again. Set the idle screw half way between. 4th step - repeat on the other side carb. 5th step - Run the bike in gear listening for any back fire decelerating (overrun for the Brits) with slightly opened throttle. If it occurs turn in each idle mixture screw about 1/8th turn. You should be good. At an idle the exhaust pulse from each muffler should be the same at this point. As you open the throttle there should not be any engine hesitation. Things that can go wrong with this process are worn jet needle/needle jet sets and plugged idle circuit.