Electronic ignition

[oldjexy]

Does anybody know how a Boyer Brandson electronic ignition makes the shift from fully retarded to fully advanced. The set up procedure is made at the fully advanced position. This must be done electronically but if the starting point is fully advanced does it somehow add a delay until the appropriate rev's are reached. Boyer seem reluctant to explain, maybe it's proprietary information, but it would sure help to know

[Ralph]

I don't know but if the battery voltage drops below a certain figure it goes to full advance.

[SPRIDDLER]

This must be done electronically but if the starting point is fully advanced does it somehow add a delay until the appropriate rev's are reached.

It's 'low and no voltage' default setting is full advance but when a voltage is sensed it adopts the retarded state. My understanding is that it knows the revolutions of the engine from the frequency of the spark and gradually advances the spark electronically according to its pre-programmed advance curve.

[shaunstaples]

I was told a long time ago it was the speed the magnet passes the coil, the faster it goes the earlier it triggers. The Advance curve is a straight line that's directly linked to engine speed. My T140 had one fitted when I bought it and would pink around 3000 revs, tried all sorts to get it/me happy but it always seemed harsh in the middle. I went back to points and set each cylinder timing separately with a timing light off a remote battery and it made such a difference, so much more pull at mid range and much smoother.
From memory, I worked out that in the mid range the boyer was about 1000 revs in front of where the points bob weights threw out, so in the middle where I like to be, it was too advanced for me. I've got friends who swear by them, just me who doesn't.

[SPRIDDLER]

From memory, I worked out that in the mid range the boyer was about 1000 revs in front of where the points bob weights threw out,

You don't mention which unit you had but the only Boyer units I've come across don't use the bobweights. The Boyer website states that one of the advantages is that by discarding the bobweight mechanism any mechanical issues are eliminated......

The advantage of this system is that engines function best with a retarded spark for starting and low revs, but need
ignition advance to run at high speed. The Micro MKIV's analogue system simply advances the spark at a set rate
from fully retarded to maximum advance, as engine speed rises from zero to 4,000 revs thus eliminating the
inaccuracy of mechanical advance/ retard units.

[shaunstaples]

Would have been an early one I guess, not sure on the model. Definitely no bob weights in my Boyer it was just a round piece of circuit board with two induction coils on it.
The bob weights I mentioned were on my points. I was comparing how far the boyer had advanced (up the straight line) at the similar revs to when the bob weights of my points threw out.

Sorry Neville for confusion, seem to be good at it!
Ps. Still going upstairs and forgetting why??

[SPRIDDLER]

Would have been an early one I guess, not sure on the model. Definitely no bob weights in my Boyer it was just a round piece of circuit board with two induction coils on it.

Sorry Neville for confusion, seem to be good at it!

As I nodded off I too was confused as it occurred to me that the OP didn't mention the year of the bike so it could be Boyer for an early mag or later coil model. However, in other posts he mentioned he has a '64 Model 18 and and a Harris G80 so this is probably his '64 Model 18 with coil ignition.

Ps. Still going upstairs and forgetting why??

I'm saving up for the new Stannah TurboLift which should get me up the stairs quicker and before I forget..............

[oldjexy]

Thanks guys , this does help a little with the understanding. I tried fitting the mk 4 Boyer few years ago but ended up taking it off because after most careful set up first kick nearly put me through the roof of the garage, it was so advanced! With this dreek winter I pulled it back out of the box and made a jig to run it on the bench to see maybe what I was doing wrong. On the bench it makes a lovely spark but probably need a oscilloscope to see if the spark advances with speed. I did hear that if the stator wires are reversed it might cause this ,again how do you test that without breaking your leg. You are quite right it's 1964 AJS18 which probably need a new advance and retard mech.

[SPRIDDLER]

I tried fitting the mk 4 Boyer few years ago but ended up taking it off because after most careful set up first kick nearly put me through the roof of the garage, it was so advanced!

Did you check that the full 12 volts was arriving at the unit? If it wasn't getting full voltage then maybe the timing was at its low voltage default 'advanced' setting.

On the bench it makes a lovely spark but probably need a oscilloscope to see if the spark advances with speed.

Could you check whether it's advancing by using an ordinary ignition timing strobe light?

[oldjexy]

I have made a jig on the bench so as to run the ignition with a drill. Works a treat and with a strobe light, that, as the speed increases, you can see a shift of 10 degrees advanced. You are right the voltage is critical if it drops to below 11 v you still get a spark but fully advanced. What is also interesting if you reverse the two wires from the coils it fires way advanced( unfortunately didn't measure it ) Either of these could have been the cause so the next step is to mount it back on the bike. Thank you for time and info it set me in the right direction.