Commando Timing Advance Curves Compiled

I've taken the liberty to compile existing advance curves from different sources and plot them on the same graph. I'm obliged to Ludwig, who supplied the TriSpark curve and much private information, and Dave Comeau, who posted the AAU and Boyer curves on his website.




1. The AAU.
The AAU curve is the gold standard for the Commando. Unfortunately, as data provided to me by Ludwig has shown, the AAU is unstable from unit-to-unit, with a low rpm (below 2000) variation of +/- 6 degrees. Dave Comeau comments in his website analysis that lubricating his AAU caused an offset of 3 degrees in the advance curve. On average, the unit gives a great curve; in practice, not so much. The unit provides low advance and start-up and tick-over (2 degrees), resulting in no kick-back and a powerfull start and idle. It is all in at 28 degrees at 3000 rpm.

2. The Boyer
As this curve is two decades old, it clearly applies only to the earliest analog Boyer units. The unit provides a very large advance (12 degrees) at start-up, likely the source of its propensity to kick-back. Advance increases to 16 degrees at tick-over and then lazily rises to only 26 degrees at 3000 rpm. Compared to the AAU, the boyer appears to have gotten things backward.

Ludwig sent me an advance curve for a Boyer Micro Digital set up for a BMW that corrects all of the above; low advance at start-up (1-5 degrees), and then a TriSpark-like curve with a tick-over advance minimum of 1-5 degrees at 900 rpm. The advance is all in at 4000 rpm. I didn't reproduce the curve here because of the large differential (5-6 degrees) between the maximum advance of the BMW and the Commando.

3. The Pazon SureFire.
Pazon is the only producer of electronic ignitions that publishes its advance curves. It features a very low (0 degrees) advance at start-up, but rises to 12 degrees at tick-over, 9 degrees higher than the AAU. At 3000 rpm, it matches the advance (28 degrees) of both the AAU and the TriSpark, but continues to increase its advance by another 3-4 degrees untill it is all in at 5000 rpm. I would expect the Pazon to provide a very strong, kick-back free start, and a somewhat weaker tick-over and low rpm performance compared to the AAU. It comes on very strong at higher rpms.

4. The TriSpark
TriSpark features a start-up advance of 5 degrees, higher than both the AAU and Pazon, although low enough to avoid complaints of kick-back. The curve has an interesting dip in it that reduces the tick-over advance to 6 degrees or so, and then roughly follows the AAU curve, but with a few additional degrees of advance until 3000 rpm, where it matches both the AAU and Pazon advance of 28 degrees. The curve dip at tick-over likely stabilizes the idle and provides a more powerful low rpm response. The TriSpark continues to increase advance by another 2 degrees until 4000 rpm, where it is all in.

I believe that the lads at TriSpark have got it right. I'm running Pazon SureFire units on my Brit bikes, and am pleased with the high-end performance, but I can feel what the curves tell me at tick-over, namely, that there is too much advance at 1000 rpm. I'd convert to TriSpark toute de suite if I could only buy their older unit with frame-mounted electronics.

I wonder where the Sparx unit falls in?

How do you explain the dip in the Tri-Spark advance curve stabilizing the idle?

I use a Pazon Smartfire, and my 11:1 comp, big valve full race motor will tick over all day at 600 rpm....never had that with any boyer......analog or digital!! I had a shorter advance curve built in so it's fullly advanced at 3000rpm, but it works like a dream

grandpaul said:

I wonder where the Sparx unit falls in?

Click to expand...

The one unit I installed was nearly identical to the old analogue Boyer for the short time it lasted. Jim

batrider said:

How do you explain the dip in the Tri-Spark advance curve stabilizing the idle?

Click to expand...

If the idle want to go down due to engine temp or mixture then the timing advances and helps keep it steady. Same if the idle wants to go higher, it slows the timing bringing the speed back down. I use the same logic in my fuel injection setup and it works very well. Jim

Thanks for posting this info Rick,
My 74 runs an analog Boyer, according to your info there is significant advance at idle speed, I believe this is correct as I have two scars on my ankle from kickback to confirm it (not kidding). I am now tempted to retard the timing to match the other curves (at idle). Unfortunately, the Boyer curve is somewhat flat and if I lose five degrees at idle I'll also lose five degrees at 3000 where I typically run. In your experience do you think that would make a great deal of difference in the way the bike will run at normal road speeds (40--60 MPH)?

Hmmmm!
Seems the more expensive units (the ones that are not Boyer) advance quickly just like points, with a little more retard at tickover.

Ah cool Commando ignition exotica!
Really savored the character of the various curves
and stabilizing swing curve for idle and off idle response.

Ms Peel has difficult scope of ignition needs and I was in dire need
of workable ranges to program it to start trials.
Wonderful to see variety laid out plainly.

One note for racer type response from old Boyers - Jim
Schimdt tells us in his Racer booklet, [what a bargain resource]
the a 680 ohm carbon filled 2 watt resistor connecting/shorting
the two trigger leads give faster advance rise racers like
for cornering exits. Must diddle timing upward again for
full advance and realize if resistor connect fail, advance
spike will blow up engine. Not good for street tameness.

What unit-curve would fit 10.5 CR 920 kick starter on 91 octane
with drag race only cam, lugging cargo up loose steeps to spanking
sports bikes both with and w/o supercharge engaged?
1st curve for easy starts and timid creeping in camps or to shed
across floating mats of muddy grass.
2nd curve for scooting about on back roads and pastures
with out booster for hi vacuum hi throttle response.
3rd curve for hi way cruise and play w/o boost nor water spray.
4th curve for maniac use of 10+ PSI boost, 116 octane fed glee.

Found this wonder, optic trigger-&-brains all under points cover,
Commando cam mount, 3 sparks each stroke, each individually
programmable into
4 curves, manual or sensor selectable each with rpm limiter.
I've pressure switches and might need Holley carb power valves
to figure out logic for spark and sprayer.

Designer brags it allowed- excessive hi CR Harley beast run
great while all the prior hi dollar famous name units
failed terrible on hi test gas- to make more power on
cheapest 87 octane than on best hi test. Low octane
packs more a punch than higher, just like a diesel, if it
don't detonate. Will be fun enjoying the journey tuning.
http://www.powerarc.com/

hobot

Yes it would make a large difference and could easily cause engine damage with slow timing at cruise speed. Jim

geo46er said:

Thanks for posting this info Rick,
My 74 runs an analog Boyer, according to your info there is significant advance at idle speed, I believe this is correct as I have two scars on my ankle from kickback to confirm it (not kidding). I am now tempted to retard the timing to match the other curves (at idle). Unfortunately, the Boyer curve is somewhat flat and if I lose five degrees at idle I'll also lose five degrees at 3000 where I typically run. In your experience do you think that would make a great deal of difference in the way the bike will run at normal road speeds (40--60 MPH)?

Click to expand...

Found this wonder, optic trigger-&-brains all under points cover,
Commando cam mount, 3 sparks each stroke, each individually
programmable into
4 curves, manual or sensor selectable each with rpm limiter.
I've pressure switches and might need Holley carb power valves
to figure out logic for spark and sprayer.

Designer brags it allowed- excessive hi CR Harley beast to
run great while all the prior hi dollar famous name units
dentonated terrible on hi test gas- to make more power on
cheapest 87 octane than on best hi test. Low octane
packs more a punch than higher, just like a diesel, if it
don't detonate. Will be fun enjoying the journey tuning.
http://www.powerarc.com/

hobot

1st curve for easy starts and timid creeping in camps or to shed
across floating mats of muddy grass.
2nd curve for scooting about on rural paths and pastures
with out booster for hi vacuum hi throttle timid response.
3rd curve for hi way cruise and play w/o boost nor water spray
for max efficiency.
4th curve for maniac use of 10+ PSI boost, 116 octane fed glee.

Hi Geo,

Just to clerify, my role here was secretarial; the real work was done by Ludwig and Dave Comeau. That said, the analog Boyer curve is simply wrong, and really can't be fixed by adjusting the offset. If you can afford a hundred bucks, buy a Pazon SureFire and be done with it. The TriSpark curve is more appealing to me, but i just can't get past the fact that the logic electonics are mounted in a 100C+ environment.

This is interesting reading. I have points on my 750 and it has a perfect 1000 rpm idle all the time, regardless of weather conditions.

I have a Pazon Sure Fire on the 850, and it starts first kick every time, hot or cold and runs very well. No kickback, ever. But the idle is inconsistent and I haven't been able to figure out why. When the bike gets half warmed up the idle goes fast, then it slows down as the bike comes fully up to operating temperature. And then the idle speed tends to vary. Sometimes a litle fast, sometimes a little slow, sometimes just right. Jetting is good, the Amals have been resleeved (didn't make any difference), and I'm pretty sure I've got the air leaks fixed (I had to use Threebond on the right manifold's heat insulator). Yet the idle strangeness persists. Sounds like the advance curve on the Pazon could have something to do with it.

If I felt like throwing $300 at the problem, it would be interesting to fit a Trispark and see if that has any effect on the idle.

Debby

debby said:

If I felt like throwing $300 at the problem, it would be interesting to fit a Trispark and see if that has any effect on the idle.

Debby

Click to expand...

Do it, do it for us! :mrgreen:

Well I have done it on both my bikes and can tell you there is a difference, The 850 started life with a Sparx unit that lasted about 5 months. This unit seemed to work ok but once in awhile it would kick back on the e-start, Then it just quit. After pulling it out and taking a close look at it I found that the solder on one of the pickups was shorting on the case, Strange it lasted that long. Changed it for a Boyer micro-digital and ran that for a couple of years also ok, But once in awhile it would stall at lights as the idle never seemed even. So then went with the Tr-spark Wow! I can tell you that it transformed the bike not only in the Idle but it seemed to have a more even power band. But the bike never kicks back now and never stalls, Knock wood! It does cost a bit more but it was so good that when I built the 72 I also put one on that bike too.

I've had great success with Sparx, but I WANT A TRI-SPARK!!!

If the Boyer is the cause of kickback its the next item going in the bin for sure.Great comparison test here cant decide which to get really as the pros and cons of each add up.

If you go to the Atlantic Green site you will find the Boyer MicroDigital ignition has a similar profile to the Tri-spark with the idle stabilisation curve, thats the theory but didn't seem to help in my case but no kickbacks with it unless the battery voltage is low which the Tri-spark can handle.

That very well may have had something to do with it, I had the 4 brush and field coil upgrade done to the starter and it was only on the electric starter that I noticed it. So in fairness I do have to admit this may have been part of it. I don't ride the bike but a couple times a month because I have other bikes that get more miles. But since the Tri-spark was installed I have not had it happen since.

Greetings,
After considering the info Rick posted I am now tempted to install points. A quick look through ebay and I was able to locate several AAUs and complete point plates for dirt cheap. Before I start bidding I thought I'd ask here if anyone has a complete point set-up that they would be willing to part with for a fair price?

GB geo46er@yahoo.com