Commando ignition timing (2015)

I believe that some of the early dominators such as the 650SS had mechanical advance on the ignition timing. I'd like to know did they have the same stroke as the commando 750, and use the same static ignition advance at about 29 degrees when running above idle ? How much retard did they give at idle ?

acotrel said:

I believe that some of the early dominators such as the 650SS had mechanical advance on the ignition timing. I'd like to know did they have the same stroke as the commando 750, and use the same static ignition advance at about 29 degrees when running above idle ? How much retard did they give at idle ?

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I'm pretty sure all 650ss models had an automatic advance. The 88ss had manual advance. From memory they ran the same advance as the Commando, but they should need slightly less since they have a smaller 68 mm bore. I believe some recommend more advance on an 850 than a 750.

Its mostly CR speed of starting combustion that determines ignition full adv, more so than the stroke. So similar CR engines will like similar timing and only one way to optimize for octane used.

I don't believe my 850 ever had an auto advance. What I am asking is how much advance the 600cc and 650cc dominators used which had the auto unit fitted, and was the stroke the same as the commando 850. If the stroke is different, it slightly affects the required static ignition advance. I might be wrong however I believe that when the bike is idling the auto advance runs on full retard, and as the revs increase the bob weights and springs cause the unit to advance to the full advance timing which in the case of the commando is about 29 degrees. I usually run a non-programmable Boyer, so the ignition timing is fixed at one value. I don't have a problem finding the optimum static timing at full advance, however I'd really like to know what range the old Norton auto advances worked over. It is engine acceleration from low revs that I am interested in.

acotrel said:

I don't believe my 850 ever had an auto advance. .

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It would have had one when it left the factory.
The stock 850 Lucas mechanical auto advance unit is marked as 12 degrees,
and the stock ignition timing mark for an 850 is 28 degrees.

Therefore at idle the ignition is timed at 16 degrees, n'est pas ?

Magneto auto advance/retard units are also marked with degrees, since they can vary.
I think Nortons either used 12 or 14 degrees, but can't see anything written on one here.
Its not much of a range of movement.
It has to be going pretty slow rpms to fully retard ?

Alan would never have figured that out....

acotrel said:

I usually run a non-programmable Boyer, so the ignition timing is fixed at one value.

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Up until last month went it finally died my bike used one of the very early type Boyer units where there are screw type terminals on the pickup plate inside the points cover not bullet connections. As you used a strobe light to set the advance it use quite obvious to see it advancing the spark as the engine speed increased. If yours does not do this maybe it is faulty due to its age.

use a Trispark Ign unit and forget, advance/retard, failed boyer boxes, "set many times" timing, hard to hide boyer boxes, excessive wiring etc etc. it really is that good! It revolutionised starting on my Snorton and made it my go to, daily use machine.
http://www.trispark.com.au/images/Class ... 2%20A4.pdf

I haven't used the strobe on my Boyer for a long time, however I don't ever remember seeing it advance itself. I would never have set it at idle revs. It is about a 1980 unit - antique, however it still works very well. As I use methanol fuel with low comp., I set it at 32 degrees static advance, then jet to that.
I think I have two ways remaining to get better acceleration - play with different taper needles, and get a decent programmable ignition module.

Of course Boyers advance with increasing rpm!

It's possible to reverse the pickup wires on analogue models and stop the timing advancing.

Range of advance on a mechanical auto advance is not critical. Don't be afraid to use a twelve degree one where a 14 degree was originally specified.

As Rohan said, pretty much all had a centrifugal advance mechanism that provided 12 degrees cam/24 degrees crankshaft advance.

From 1960 and 1968 Service Manuals:

Model 88 - Full advance 30 degrees, full retard 6 degrees.

Model 99 - Full advance 32 degrees, full retard 8 degrees.

Note: Most models had auto advance, but certain 650 SS models had a manual advance.

750 Atlas - Full advance 32 degrees, full retard 8 degrees.

From 1969 and 1975 Commando service manuals:

Commando, all (except PR with optional Boyer ignition) - Full advance 28 degrees.

From PR Service Notes:

Commando PR with optional Boyer ignition - Full advance 30 degrees (no rpm mentioned, but presumably at 5000 rpm).

As Triton Thrasher pointed out, all Boyers have built-in electronic advance, unless you connect the pickup wires reversed, in which case the advance is disabled.

Ken

Thanks Ken, I'll have a look with the strobe to see if it advances with the pick-up wires reversed. When I bought the unit, I simply fitted it in accordance with the wiring diagram. the leads may be the wrong way around. If I reverse them and it advances, would maximum advance still be 28 degrees ?

acotrel said:

I think I have two ways remaining to get better acceleration - play with different taper needles, and get a decent programmable ignition module.

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Do you use low rpm in racing much though ?
The mechanical advance unit is fully advanced by 3000 rpm.
Which is just idling rpm in a race bike ?
And would only be retarded a trace in these leccy ignitions.
The gains could be very modest indeed....

The retardation mostly only gives the mechanical bits an easier life, and the rider a softer ride,
the performance would be stronger with full advance all the time ?

Anyone dynoed a motor on full advance all through the rev range ?

acotrel said:

Thanks Ken, I'll have a look with the strobe to see if it advances with the pick-up wires reversed. When I bought the unit, I simply fitted it in accordance with the wiring diagram. the leads may be the wrong way around. If I reverse them and it advances, would maximum advance still be 28 degrees ?

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Not sure I understand your question. Maximum advance would depend on where you set it. Boyer's instructions are to time it at 5000 rpm, and they don't give any specs for timing it at lower speed, except for the initial mechanical timing. As I recall the early analog Boyers had a total advance of something like 19 or 20 (crankshaft) degrees at 5,000 rpm. It does continue to increase with rpm, so if you set it at 31 degrees at 5000, as Boyer recommended, you'd be up to something like 33 at 6000, and 34 - 35 at 7000. The numbers aren't too precise, because the advance curve isn't quite linear, but you get the idea. If you set it at 28 degrees at 5000, you'd be up to 31 - 32 at 7000. At that setting, you have about 13 degrees advance at a 1000 rpm idle, and close to 10 at kick starting speed. Most of this info, including advance curves, is available on Dyno Dave's web site. He did an extensive evaluation of Boyer ignitions some years ago. All this applies to the old analog Boyer. If you have a modern digital version, it is quite different.

Ken

If you static time a Boyer to 31° it will never advance past 31°, no matter how high you rev it. All the circuitry can do is retard the setting at low rpms, it cannot fire the ignition before the magnetic trigger is aligned on the pickup plate.

"truck driver, heavy equipment mechanic, rescuer of carpentry, old bikes, old cars"
What, no electrical engineer?

mikeinidaho said:

If you static time a Boyer to 31° it will never advance past 31°, no matter how high you rev it. All the circuitry can do is retard the setting at low rpms, it cannot fire the ignition before the magnetic trigger is aligned on the pickup plate.

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Are you making this statement for proper normal wiring?
I wrote these articles cause I hate to type the same old SHITE over and over.
http://atlanticgreen.com/boyerexposed.htm

http://atlanticgreen.com/boyerevolved.htm

The maximum advance you can use is limited by the knock-rating of the fuel, the compression ratio and how lean you can run the jetting without doing damage. The three things constitute a balance. The taper on the needle compensates for loss of vacuum which can cause the mixture to become leaner and cause detonation and damage. My feeling is that the optimum ignition advance curve is a function if the internal geometry of the rods and crank which affects the rock-over time, and also the fixed time of the combustion event at any given comp. ratio. It has been claimed that it is impossible to derive the optimum equation for the advance curve. I don't believe that. But it indicates to me that most of the advance curves which are available in off-the-shelf units are at first arbitrary - probably guess work, then modified from experience from use with various motors. With the Dynatec ignition systems used on Harleys, there is a purple lead which can be used to attach to a vacuum switch in the inlet port. If vacuum is lost, it switches the ignition to a less aggressive advance curve. In most cases the purple lead is not attached to the vacuum switch, so the advance curve never changes.

Guess you didn't quite understand what I was trying to say, it can't fire the coil before the trigger lines up, same as a set of points don't fire before they open. If it's firing at 35° at 5,000 rpm(or whatever rpm it is fully advanced) it was static timed at 35°at 0 rpm. Wasn't intending, in any way, to question your superior knowledge in all things Boyer, just stating obvious fact. No need to get the measuring tape out again, I'll go quietly.