tech7

Boyer electronic ignitions seem to be very controversial.
The reasons escape me because in four separate installations, all from
scratch, I have yet to have a problem with the Boyers. On the Internet
I occasionally see "Help" requests from people having serious problems
with them. Or that's the way it seems until I delve a little deeper to
find incorrect installations or other bad components in the system.
Sometimes these troubled people destroy the Boyer due to ineptness,
hardly the fault of the Boyer ignition.

Boyer makes two distinctly different electronic ignitions. The old
standby, in who knows which current iteration number, is the analog
electronic ignition. This version can be used in a batteryless system
as the initial startup conditions does not require any voltage on the
ignition module. The latest version is the digital electronic
ignition. This, of course, represents the ignition of today (being
digital) but the serious drawback to me is that the battery must be
there for startup and be fairly well fully charged. Let's start with
the Boyer Digital Ignition, but with minimal details as I have no
direct experience with Boyer's version. My 30+ years in electronic
digital design engineering qualifies me to at least hit the high
spots. I'll say up front that my preference is for the analog unit as
it is more forgiving of any charging system problem, like low voltage.
Also note that much of this explanation of these systems is based on
experience with other electronic ignitions as I am not privy to the
exact circuit implementation used by Boyer.

Boyer Digital Ignition Overview:

The Boyer Digital works on the principal of a typical computer. There
is a triggering device that runs off the shaft that previously housed
the points cam. There is an electronics module, epoxy encapsulated for
elements protection, that houses the "computer". The key to any
computer working is its' clock. Usually it is a quartz crystal
controlled device (but not necessarily if accuracy to the millisecond
is not required) that acts as the impedes for all operations within
the module. The time interval between clocks pulses is fixed and can
be used to measure frequency and through calculations, time. The
computer uses the engine timing trigger signal, timed to be before the
earliest possible advanced point, to start a delay timer. It counts,
using the clock, the time between trigger signals to determine the
engine RPM. It knows RPM and the early trigger point. It keeps an
internal chart that specifies the spark delay from the early trigger
point to the actual plug firing point verses the engine RPM. Some
times there are multiple charts available and you get to choose. From
the point of generating that spark trigger signal to actually
generating the spark, the generation of the actual spark is an analog
function which will be covered in the analog version of the Boyers.
The Digital version allows critical timing, variable timing by
predetermined switch selection, and a modern sound to the name for the
sales literature.

Boyer Analog Ignition Overview and Details:

First of all this device replaces the points, the mechanical advance,
and the condenser. These are all the mechanical parts of the original
Lucas system that can be troublesome, as all electromechanical devices
typically have the highest failure rate in any electrical system. The
Boyer includes a small electronic module, encapsulated in epoxy for
protection from the elements. It also includes a magnet assembly that
fits into the position in the points cover previously occupied by the
points cam. It is designed to fit the taper on the shaft where the
points cam used to fit. And finally, it includes the magnetic sensor
trigger coils that are part of the new epoxy resin circuit board that
fits where the circular points plate formerly occupied. The circuit
board is slotted, as was the points plate, to allow minute adjustments
to the full advance timing.

As the trigger magnets swing past the trigger coils in the points
cover a relatively slowly rising voltage is generated. This trigger
voltage will rise more quickly with increase RPM. The analog circuitry
looks for the rising voltage to cross a threshold voltage, later if it
is slowly rising and earlier if it is fast rising. This difference can
give the automatic electronic advance feature without mechanical parts
and pieces. This is the spark trigger signal. From here on the two
units, analog or digital, could be the same internally.

These units are capacitive discharge ignition devices. Some internal
electronic circuitry boosts the battery's 12 VDC to the neighborhood
of 300VDC. A capacitor slowly (relatively) stores up a charge from
that 300VDC source for use by the spark plug. When the spark trigger
is generated it triggers a solid state device like a Source Controlled
Rectifier (SCR) or perhaps a switching transistor to deliver the
charge fast (relatively) to the engine's coil. This fast buildup of
the voltage on the coils primary terminals results in a transformer
action by the coil resulting in a potential voltage at the plugs in
the order of 20,000Volts, which easily jumps the spark plug gap.

The capacitive discharge system differs from a battery ignition system
which supplies 12 VDC to the coil, saturating the magnetic field of
the coil. The spark plug of the battery ignition system does not fire
until the points open allowing the magnetic field to callapse and
oscillate with the condenser generating the 20,000 volts required. The
difference in these two systems is that the capacitive discharge
system is more efficient with the use of the battery power and the
spark at the plug is 10 to 100 times faster in discharge. That reduced
time reduces the opportunity for the 20,000 volts on the plug to be
bleed away by the deposits on it before firing. Hence, capacitive
discharge systems tend to be more foul proof. In fact the spark is so
short and physically narrow that it sometimes is hard to see the spark
in bright sunlight. But that doesn't mean it is not there containing
the same or more actual energy to get the flame burning in the
cylinder.

Installation is usually quite simple. First you must remove the
points, and the points cam with its mechanical advance unit. A bolt
inserted into the end of the cam and wiggled usually get the points
cam off its' taper. Install the new magnetic assembly on the points
cam shaft as per the excellent instruction, then the trigger coils to
the former points plate mounting point. The static timing as per the
instructions is easy and actually very accurate. Mount the
electronics and wire the system. Keep all the ignition wiring separate
from any of the alternator wiring and the trigger coil wiring
emanating from the points cavity separated from all wiring, twisting
the wire pair to about one twist per inch for its' entire path. Carry
the ground for the module all the way to the battery if possible.
Don't rely on the frame or motor as a return path if possible. Make
sure that the motor is adequately grounded to the frame for the spark
plug and for the coil return paths. For twins you are best served with
two 6 volt (yes, 6 volt) coils wired in series and for singles a 12
volt coil is correct. In twins both cylinders fire at once, one on the
compression cycle (normal), and the other on the exhaust cycle (not
normal but doesn't effect anything). This approach on twins keeps from
having to buy two Boyers, on for each cylinder. Boyer Analog Ignition
Systems do have limits on minimum and maximum supply voltages and
minimum and maximum coil resistance. PVL coils match those
requirements. When the installation is done you can accurately adjust
the timing by moving the circuit board in the points timing cavity
while strobing the timing mark on the alternator rotor with a timing
light.

Well, I hope that some of you might be convinced to take the Boyer
leap. In the long run you win: no maintenance and consistent timing
virtually forever.

After writing this I found out that the analog Boyer is not a CD
system but a simple transistor ignition where the points and condenser
are replaced with a transistor switch. It still has advance but it is
a bit crude compared to digital advance. All the advantages of fast
rise time are not in the analog Boyer and only in the digital Boyer.
In defense of the analog Boyer, it has been around for decades, works
well, and has exhibited excellent reliability. Bikes with correctly
installed Boyers run very well, normally, and once installed rarely
need anything more done to the ignition. The added complications of a
digital designed ignition would probably be wasted on a Brit bike
anyway.

Addendum:

It turns out that not even the Digital Boyer uses Capacitive Discharge
for driving the coils. It too uses the transistor switch arrangement.
But it does use digital techniques to do the spark advance. It also
turns out that it is highly sensitive to Electro Magnetic Interference
(EMI). The “computer” in the Boyer Digital unit gets very confused when
noise from the ignition system is excessive so either resistor plugs,,
resistor wires, or resistor plug caps are required (but only one of
them, not all).