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| I originally wrote this in October 1989. It was
published In the NNENO News (Northern New England Norton Owners) in April
1991. It was re-released in Norton News (INOA) in issue #93 summer 1991.
At the time it did generate a lot of mail and phone calls to me, but then
I was surprised to find, when I very reluctantly came into the internet age, that my article had been talked about so much on the BI list, and had found a new "home" on the captain norton web site, Vol 3. Welcome to Captain Nortons Home Page
I've made a few typo corrections that had crept in but otherwise I've left it as original as possible. DJC
My first Commando, bought new in July, 1970, was an unmitigated disaster. In September, 1987 I bought my second Norton Commando, a '72 Combat, and to insure some useful life for this motorcycle, I have been studying everything I can get my hands on. I've learned quite a lot in nineteen years, part of which is patience and skepticism, and part of which is the subject matter for this writing, that being ignition characteristics, primarily those of the Boyer.
The general consensus is that the factory Lucas centrifugal advance points system is bad, and the Boyer / Lucas Rita systems are absolutely great. I want to know why, for both cases, but I will sometimes refuse to accept "parroted" endorsements due to lack of factual substance. An example of this is the lack of any advance curve specifications for both the Rita or Boyer.
I understand that early 750 Commandos, Combats and low compression 850's with a Boyer installed will run down the road under their own power. I also accept the contention that the Boyer is likely the best 'consumer' product as of this writing. However, having had a substantial amount of ignition curve tuning experience to know of the power and drive ability improvements that can be made with proper attention to detail, and what a pig a motor can be in the timing is too retarded, simple agreement with the concept that one advance curve fits all is too much 'Black Magic' from the 'Black Box' for me to accept.
There is some existing information on the stock points system and an excellent two part article on the Rita by the Chicago Norton Owners Club. (Strangely only part 1 was in NN68 Pg. 19.) Part II was excellent. But no one had any in depth information about the Boyer! There was no advance curve data. I was interested in finding out what the advance curve was and if it is possible to tune it. I had bought a new Boyer but was reluctant to dissect it because if I damaged it, I wouldn't be able to try it out. I even had an offer from two guys in the BSA Owners Club of New England, Ron Pare' and Armand Poitras, to split the cost of a Boyer three ways and let me take it apart for analysis. Then Pete Kogut gave me one that was dead, new, right out of the box. I had my "victim" and this is what I discovered inside that:
Depotting a Boyer completely is no small feat. It took about six hours using paint stripper to remove and catalogue all the parts. Its not worth depotting the circuit except to replace the output power transistor, especially in light of the extended warranty. The power transistor is, however, the easiest to depot, and in the case or Pete's box, this transistor was indeed bad. (I want to thank Pete Kogut for the dead Boyer and Peter Martin from the North Florida chapter for knowing of and sending me a copy of the Rita article.)
The pickup device consists of the CCW (Norton) rotating magnets and stationary coils T1 and T2. They produce a single sign wave per coil firing that starts with the negative going portion first. The amplitude increases as rotational speed increases (RPM's).
Diode D1 clips (shorts) the positive portion of the sine wave to .6V. Varistor RT1 helps to keep the timing consistent to compensate for D1 heating up causing timing drift due to D1 resistance change.
The transistor circuit around Q1 is an integrator that creates bias that goes up or down proportional to RPM. This bias aids the advance curve and is a key feature that sets the Boyer above the Rita.
The negative pulses are added on the bias to trigger the high speed switching circuit Q2 / Q3. Q2 (is caused to) shuts off causing Q3 to conduct; feedback resistor R7 provides regenerative feedback and initial biasing for Q2. The output of Q3 is feed to the base of Q4 which is an amplifier.
Transistor Q5 and Q6 normally conduct, the current of Q6 passing through the coils. When these are made to cut off, the coils will fire.
As this circuitry fires with a negative pulse, diode D3 and capacitor C5 shorts out the negative pulses feeding back from the ignition coils and prevents the re-firing of the circuit.
The ignition coils must always be hooked up between black and red, irrespective of whether you are using the Boyer in either positive or negative ground configuration. (The most likely difference in a BSA / Boyer hook-up is that the black/yellow and black/white leads are reversed due to Clockwise rotation of the magnetic rotor. (The negative pulse must always come first).
In NN74 Pg. 14, Brian Slark says to put a ballast resistor the white wire. I disagree. My analysis tells me the proper place, if you were to use a ballast resistor, is between the black wire and the coil. It is not desirable to reduce voltage to the whole Boyer. Not to say that it wouldn't run anymore, but since the timing is related to voltage, the timing may go spastic in order to follow the fluctuating voltage. On a similar concept, if diode D3 was a Zener, it might help improve the stability of the ignition curve against voltage variations.
I did not spend too much time analyzing the circuit in minute detail, and since the depotting process was difficult at best, I feel only moderately confident of component size and location. I did look at wave shapes with an oscilloscope with the de-potted Boyer on a Sun distributor machine. The Boyer ignition curve was taken from a new Boyer right out of the box. The Rita curve was taken then followed by the points type system from my '72 Combat that appeared to still be in fairly good condition.
To the uninitiated, the way to look at a distributor curve is to be, (1) very aware these are distributor degrees and distributor RPM, and that there is no such thing as initial advance until you install and set these components on an engine. Only at that point should you talk in terms of initial timing and engine degrees. The timing would then be 2 times distributor degrees plus initial advance).
Therefore, all three distributor curves are zero advance at zero RPM. These curves are presented as being reasonably representative of each type of ignition system and unless proven to me or by me as otherwise, I accept them as fact.
Since I have not yet been able to gain access to a dynamometer, let it be understood that the following is strictly my own personal opinion as to how these devices should be utilized. This is simply Ford vs. Chevy argument stuff and I will listen to and give consideration to all other arguments. My conclusions are derived from my understanding of how ignition curves are developed based upon how dynamic engine pressures are effected by compression ratios and cam timing. Given that these parameters are different within 750, 850 and 750 Combat motors, and that ignition curves for the Boyer and the Rita are different as shown in the chart, I will use the Rita on my Combat and the Boyer on my 850. On my '71 750 (pre combat) to be assembled at some future date, I will more than likely use the Rita also, with a little more initial advance than the Combat.
My next project is now underway to produce a centrifugal advance unit with modified rotor which will use two Chrysler can electronic ignition pick-ups (just like Lucas Rita) and fire two Chrysler car electronic ignition modules that in turn fire two coils. Each coil will fire only one at TDC compression respectively. I believe I've heard of someone out there doing this before.