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slug Offline OP
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hi may be a silly question. with ignition switch on
bike the central position is off. there are two other
position ign on and emg on.think the emergency position
bypasses battery and takes feed from stator direct.
switch is the standard sa66 . when fitted is the key postion
switch down on. and key turned up emergency.
cheers the slug.

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S
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Hi,

Originally Posted by slug
hi may be a silly question. with ignition switch on
bike the central position is off. there are two other
position ign on and emg on.

From the '65 B31/B33 (which appear to have the same switch) Instruction Manual on Kim The CD Man's BSA CD:-

"Ignition Switch

In the centre of the lighting switch on the headlamp cowl. It has three positions: Off, Ignition and Emergency. Insert the ignition key and turn to the right before attempting to start the engine. If, for any reason, the battery is exhausted turn the switch to the left then start the engine in the normal way. As soon as the engine is running at a moderate speed rotate the switch rapidly to the normal ignition position when it should continue to run normally.".

Originally Posted by slug
think the emergency position bypasses battery and takes feed from stator direct.

Not really. In 6V systems, the battery (crudely) performs the task of volt/current regulation. Any Lucas single-phase alternator has six stator coils, connected together as a pair and four. When the bike's running without lights, the pair of stator coils generally provide enough power to run the ignition and keep the battery charged for times of low-rpm running, when the two stator coils don't provide enough power on their own to run even the ignition.

Using the lights obviously requires more power so, when the lighting switch turns them on, it also connects in the other four stator coils. The "Emergency" position also does this but, if you aren't using the lights, once the additional power's charged the battery, it'll simply go on to overcharge it, eventually boiling it dry. frown

Originally Posted by slug
when fitted is the key postion switch down on. and key turned up emergency.

A picture in the aforementioned Manual shows the key slot vertical.

Hth.

Regards,

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slug Offline OP
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hi stuart thanks for info. my switch is located on tin ware
behind engine where battery is.the switch is a new replica
item. normal switch positon is horizontal thats the off position.
by turning key to right that is my up positon so should
be normal on.so if i turn key to left that would be my
down position emergency battery low position. like you saw running bike in emergency setting would cause battery to boil.
think i read some were that if you ride with switch in emergency position engine will after a time start misfiring ??..any one else come across this.
cheers the slug.

Last edited by slug; 11/18/12 7:28 am.
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Yes, a long time ago though, if my memory serves me correctly once the battery gets a bit of charge in the emergency position the bike starts to missfire, thats the cue to flip the switch to normal. Its hard to kick start in "emergency" , the drill was run and bump to start then after a few hundred yards switch to "normal". MZ two strokes had a similar scheme that was my last experience of this quaint system.


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