by David Comeau, Jan 2001
u/d Jan 2004
I have long been interested in engine tuning. Ignition and carburetion
issues seem to be the most challenging to most motorcycle hobbyists and
mechanics. I have had the good fortune to have ample schooling in physics,
electromagnetics, electronics, flow dynamics and mechanics to somewhat
tie it all together. I want to mention this article is not intended to
be a beginners introduction to ignitions. Many topics and data are more
easily interpreted by persons with the needed technical background.
That is why my explanations may seem rather short, since the data should
speak for itself.
The evolution of commercial electronics has allowed the packaging
of various commercial ignition products for our British bikes. The
investigation of these systems is quite natural for me, as it is similar
to the work that I do everyday. As the Boyer Mk III seems to
be phasing out and being replaced by the micro-digital and micro-power
systems, I wanted to first review the old systems and second,
press forward with a fresh look at the new technology. I felt it
would only be fair to take another, and closer, look at the Lucas
Rita (Racing Ignition Transistor Amplifier).
Some of the things I wanted to review were the high voltage
spark potential, system current draw, pulse stability, and especially the
advance curve. I still believe that one advance curve is still asking too
much black magic from these silver, black or red boxes. I even included
in the test, a few non-Norton devices for advance curve comparison purposes.
I was astonished by some of the comparisons. The comparison
of like systems, showing production consistency, only caught my eye as
the tests proceeded. The system operation under electrical duress
(low voltage) was especially important to my test, considering the Norton
Commando E-Start start/no start and the potentially damaging kick backs
that I have seen so often on other E-Start owners bikes. The upper limit
of 14.3VDC was used for all ignition systems, since this should be the
charging systems zener voltage and therefore the regulation point for the
Norton’s electrical system.
In this series of tests, since I did not own the MD and MP samples,
so I did not depot and reverse engineer these new boyers, which I
had done in my Boyer Exposed article of Oct 1989. The purpose of this research
was not to discover trade secrets, but verify application suitability of
these systems, and general technical specifications.
The Test Equipment
1954 SUN Distributor machine.
A little refurbishment was required as the capacitors were 46
years old and were electrically leaky, these were replaced. The rectifier
tube was replaced with high voltage, high current diodes. My 700vdc xenon
bulb strobe power power supply was now ready.
The electric tachometer was checked for accuracy.
Its readout upper limit is 2800 distributor rpm. That equates to 5600 engine
Dynodaves little brute DC power supply.
Built in 0-30 vdc meter and 0-10 Amp (checked at
cal lab to NIST)
I had to build a brute power supply with a bit of filtering to allow,
adjustability, average and surge current demand and keep rectification
ripple out of the ignitions themselves so I wouldn't be measuring power
supply ripple in my tests.
Ignition O-scope, real time-self adjusting time base.
Textronics 465B O-scope
Voltage probes of 1:1, 10:1, 100:1, and 1000:1
Additional voltage and current measurements with Simpson 260 series
8 , Simpson 460, Triplett 310 type 6 and SnapOn MT402 .
Boyer MK III Production variations
Of significant interest to me was the variation I found among the
three brand new samples I own. Show below is raw data.
When each of them is installed to 31’ on an engine, they will
have 5’ starting timing difference.These production variations alone could
explain why some nortons when set up by the prescribed procedure have no
pinging problems and another bikes timing must be retarded to get satisfactory
Recently, I have reluctantly become convinced
the tri/bsa boyers are intended to have the same curve as the norton unit.
To include the bsa/tri curve to the 3 norton devices I have already tested,
bodes poorly for the MKIII. I would assume that boyer ships
ignitions that meet there specifications, and if that is the case then
these 4 curves indicate the broad spec that passes for acceptable.
Boyer analog on engine (now includes
ADDED Dec 2003
A later version has been updated to include newer style components.
The following diagrams were generously offered to me for display.
A TO-220 darlington replaces the old TO-3
style, probably zeners across the output transistor to prevent
overshoot from damaging the output driver
Many wild claims as to the current draw for the boyer
have been proclaimed. So I made some measurements.
The first measurement was basically with the distributor
machine at idle speed, then the current draw throught two stock 6V commando
lucas coils. See coil descriptions for details. Of course, other
coils would not give exactically the same results, but would be proportional.
The measurement was at the 14.3vdc voltage from idle then
increasing the speed to full running RPM with the current noted.
The coil drive on-time % goes down as the whole ignition cycle “time”
gets shorter. This results in a ever decreasing duty cycle and therefore,
average current. This is likely the opposite effect of what is really desired.
These current measurements are the result of averaging
together the peak current during coil drive on time and zero current during
off time. Otherwise, in non-ignition electronics terminology this
on/off ratio would be called called duty cycle.
Boyer analog current draw and duty
Boyer MK III (analog)
Voltage Duress induced Spark Jitter
I was curious to find out how low, in supplied voltage, the boyer
would continue to operate and provide a spark. The test I performed
was to provide a decreasing voltage to the box while running the
distributor machine at basically a cranking speed or low idle. I was surprised
to find that as the voltage was run down, the boyers output started to
trigger the spark in an erratic advanced and retarded display of timing
(jitter). So the claimed lower limit of 10.8vdc, for “proper” operation,
is verified. The spark jitter is of main concern primarily for E-start
machines where an over advanced ignition pulse may cause kick back.
Of course the E-starts ignition low voltage is caused by the use of the
starter and then loads the battery down. There is then the additional line
loss between the battery and the ignition module.
A fellow with a BSA twin Boyer with a low battery, who broke
his ankle in front of his bar buddies, may also be interested in this data
as to why the kickback/backfire may have happened and then causing some
discomfort and embarrassment.
The ignition ultimately quit sparking at 6.5 volts.
Boyer voltage duress jitter
Lucas Rita- Electrical Duress, Jitter, Current Draw, Advance
The ignition module was subjected to electrical duress at
an idle/starting speed. The coils used were the same stock Norton commando
6V units. The LR made consistently repeatable timed pulses until
finally at 5vdc, the unit quit making sparks. It had NO visually
observable voltage duress induced jitter.
The biggest potential flaw I have found with the LR is that the
rotor supplied does not always seat reliably in the taper of the camshaft.
Then as the LR rotor wobbles the gaps differ between the two rotor tips
and the stationary pick-up. This causes the two cylinders to fire at different
degrees. On mine, once both gaps were made the same by filing one rotor
tip the firing was absolutely the same for both cylinders.
The LR “is” electrically the hungriest ignition unit tested.
The Lucas Rita current draw changes very little as the RPM goes up, it
does go down slightly due to decreased duty cycle.. The coil drive
is off for a fixed 0.16 milliseconds. When the LR is cold, With the stock
coils it draws a little over 3amps. As it warms up, at 14.3vdc it draws
2.7Amps reflecting the high coil drive duty cycle that is 99.2% at idle,
and reduces to 98% at 5000rpm.
The production repeatability appears to be quite good as evidenced by
the advance curves from my two spare units. Despite the added cost, these
are by far my favorite.
Lucas Rita for Norton
Boyer MicroDigital- Coil Drive Dutycycle, Current Draw, Timing
This ignition was run up on the distributor machine and when
2850 rpm was reached the spark intensity visually went down. This certainly
sparked my curiosity. A look at the voltage supplied to the coil quickly
showed the reason for this phenomenon.
The coil drive control is quite simple. However, this digital
coil drive must be thought of in terms other than conventional dwell and
therefore is not expressed in degrees.The coil NON drive time is fixed
in a series of stepped time periods.
Starting mode appears to be 9 milliseconds of coil drive OFF
time before the coil drive voltage is turned on in preparation for firing.
From 250/500 rpm to about 2200rpm, the next coil drive OFF time is
reduced to a 4 milli second period. Thereby increasing the coil drive ON
From 2200rpm to 2850rpm, the next step for coil drive OFF time is reduced
again to 3 millisecond period, again increasing the ON time.
At 2850rpm the coil drive OFF time is decreased quite a bit to .5 milliseconds.
At 2850 distributor RPM the sparks visual intensity goes
down. What gives? My theory is as follows. Well, I noticed that a spark
plug quite frequently sparks a second and sometimes a third time upon shutting
off the coil drive. When left alone, the coils tank circuit primary continues
to oscillate, but when this last step (.5Msec coil drive OFF time)
is achieved the coil drive is turned back on during the period these “residual”
sparks might otherwise occur. This obviously eliminates any possibility
for these residual sparks to occur. The coil is not allowed to cease oscillation
on its own. The coil drive is turned back on right away right after the
first plug firing. You no longer see the second or third spark so the visual
effect is then understood.
Boyer MicroDigital dutycycle
and current draw
The operating advance curve data that I obtained was virtually
the same as what they published.
Boyer MicroDigital advance curve
Their published literature stating control of over timing angle (advance/retard),
ignition coil energy, tick over stabilization, and rev limit. Are now better
The meaning of their term “starting speed”still eludes me. Their ability
to custom make a curve to order is a very good feature.
Boyer Micro Power
I almost missed the opportunity to test this device by not
being fully aware that the micropower was different from the microdigital.
This little “red” box is easily confused if the name is not specifically
refered to. This device is in fact very different and I found it also very
This “other” little red box must have some of the same
circuitry of the Micro Digital. The advance curve seems to be the same
as the MD. The trigger pick-up is the same one as the MK III and
the MD Boyers. This is where the similarity ends. The output section of
this device seems to have its roots back in the 70’s. It appears to be
some sort of a capacitive discharge similar to the big SCR CDI’s of yesteryear.
It has an internal 12-14.3vdc to 400vdc converter. This is evident by the
400volt 12-20 microsecond pulse shot out of this box to the coil. The 400vdc
output seems to be quite well regulated as the output voltage stays stable
even with a varying input voltage and across the RPM range which also affects
the loading of the power supply/converter. This type of regulation is easily
obtainable with a pulse width modulation integrated chip controlling the
width of the driver circuitry running the step up transformer.
The 400vdc output pulse seems to be width controlled and may
differ from the old SCR CDIs of yesteryear that would totally dump the
complete capacitors charge. This unit may possibly be J-FET controlled
on the output stage. Just guessing of course!
The power consumption is quite minimal and would be the best
thing going for a total loss race bike ignition system. A small battery
would likely run this system for a full days racing. It was only drawing
.2 to .3 amps while running at speed and only pulled 1.2 amps during startup.
A conventional 12v coil saturation type system is very inefficient and
heat is its biggest product and only a little of the energy goes into spark
The special coil needed for this system is electrically similar
in characteristics to a conventional coil. The most obvious technical difference
is that, unlike a conventional coil, the secondary is totally isolated
from the primary.
This an exceptional little unit that I would like to try
on my Norton someday. I would like to have a different curve however. This
unit tested was actually a Triumph/BSA unit. People who have
this system have raved to me about it. I feel they may well be justified
in their praise. The installation instructions are basically the same as
the earlier Boyers. I was at a loss though, to find any suggestion in the
accompanying sheet as to what it should be timed to.
Boyer MicroPower advance curve
MicroPower REVISITED Jan 2004.....
The unit I depotted this day is marked Boyer "micropower". A
closer look at the internals shows
technical characteristics that did not seem obvious at first look.
The first notions I had, about how it worked, were giving it more technical
capability than I thought. The actual circuitry
of this device shows that it may be a short dwell device giving the output
darlington transistor the ability to keep it's heat disappation load (duty
cycle) down to a manageable level. This characteristic would explain why
standard coils would not function well with the MP. It then gains the ability
to run a higher current (lower resistance) primary coil that will transfer
the energy into a hotter spark, without the heat of a long dwell system..
It's 400v pulse was actually the 3-130v zeners clipping on the inductive
overshoot of the coil. It was NOT the drive pulse itself.
The MICROCHIP PIC16C56
XT I/P microprocessor , clocked at 4Mhz, does the calulations to sense
the timing triggers then derive the delay for the output switching.
board-foil side BB018
In final assessment I wonder how boyers litertature that stated a 400v
pulse is the output of the micropower can be true. This unit , driven through a load resistor instead of a coil, shows it
is only switching the 12v source supply. I wonder if it was mistakenly
packaged and labled?
Lucas Mechanical Points- Advance curve, Current draw
The mechanical advance curve accuracy and repeatability is primarily
a slave to its mechanical condition and lubrication maintenance. It’s supposed
virtue of mechanical simplicity is also its achilles heel. The graph easily
demonstrates this. The graph below shows the mechanical advance difference
with and without oil. The extra 3 degrees advance is for separating the
two curves for visual clarity, and it also shows what it would be like
if installed on the engine. 15’ distributor would be 30’ on the engine.
The extra 3’ would be 6’ initial timing on the engine. The oiled mechanical
advance would be the most prone to pinging since it advances quicker
mechanical points advance curves
This system draws a steady 2.6 amps @ 14.3vdc and was tested
with stock commando (71 and up) 6 volt coil configuration with ballast
resistor. Each set of points were closed 44% of the time. Each coil runs
separately but only one quarter of the total power is consumed by each
of the two coils. The ballast resistor makes heat with the other half.
Additional Motorcycle Advance Curves
comparison of points/boyer analog/lucas
rita/ boyer digiital
Bob Patton-loan of Boyer MicroPower for testing
Steve Shivers -loan of Boyer MicroDigital for testing
Micheal Moore of
Euro Spares - Electronic Components
for the loan of Lucas
Ritas to test