Commando Timing Advance Curves Compiled (RevA)

I pinched Dave Comeau's advance curve for the Boyer MicroDigital and added it to the graphic (most of Dave's links were showing as "broken" when I did the original comparison).



The MicroDigital looks pretty good. Dave did not have a start-up (0 rpm) advance, so I took it off of the BMW MicroDigital data provide to me by Ludwig. This curve has tick-over stabilization and follows, but lags, the AAU curve. At 3000 rpm the MicroDigital provides 3 degrees less advance than the AAU/TriSpark/Pazon. Like the Pazon Surefire, it's all in at 5000 rpm with 32 degrees of advance.

Any MicroDigital users out there who can comment on start-up, tick-over, and low-speed performance?

Andy Perkins at Pazon tells me that Pazon is about to introduce a semi-programmable unit that will include a tick-over stabilization curve, priced in between the Surefire and the SmartFire. Pazon, it appears, actually listens to its customers.

The AAU curve is easily the best curve. All the e-ignition makers have to do is duplicate it. Either boyer is horrible for kickstarting. The Pazon is quite good but the total comes in too late. The Trispark is, IMHO, the best compromise of the E ignitions. The points/AAU is the best performer...

The Boyer is NOT horrible for kickstarting.
Mine NEVER kicks back & usually starts 1st kick.
Where were all the others when Boyer was about?
I think we are splitting hairs here.

I'm with Flo on the Boyer experience. Apart from AAU points which were fine when new, but terrible when worn I have not tried any of the others so I defer to others views based on usage. Graphs aside, what I have found in my Boyer, which is now 25 years old the original analogue unit is that my Mk2 850 with a single 34VM Mikuni starts 1st kick and settles down to a solid idle hot or cold. The other bike, also an 850 Mk2 has the same Boyer model but new dual Amal Concentrics. It also starts either 1st or 2nd kick and has a good idle. Both bikes accelerate well and run nicely. So, the question is - what the hell does a graph tell you that implies a superior product? If it starts 1st kick, idles well and runs well , then how does one substantiate that one ignition product is better or worse?

One thing I believe that is missing from the debate is the quality of fuel. I do believe that lower RON gas or high E content makes starting and idleing problematic. The stuff just explodes too fast. That is one contributing factor where the lower starting degrees, i.e. 5 BTDC is an advantage. In that respect, I would be happy to fit, if and when my old Boyer finally dies, one of the other products.

Mick

I have the MicroDigital and a Commando and on a Victor, on the Commando it replaced a EI which used to AAU to trigger it and it works well in comparison. On the Victor it replaced a Boyer analogue and cured the pinking at 2-3K rpm which is confirmed by the curves on the graph (assuming the curves for the Unit Singles follow the same pattern). Only issue in comparion to the Pazon and Trispark is the over advancing at low batery voltages, can live with that but will not be fitting any more analogues.

"how does one substantiate that one ignition product is better or worse? "

In this case it's actually quite simple. First, you want as little advance as possible at start speed, especially for kickstarting. Second, a four stroke engine in the operating RPM range of our Nortons produces it's best response (power/torque) when the maximum ignition advance is all in by around 3000-3500 RPM. That's all the ignition has to do and it is exactly what the points/AAU does because the designers knew that was the best ignition curve for power.

NOW...it is true that the best curve for overall power can cause detonation with poor fuel. That's the reason that, back in the day of non-computer-controlled engine management systems, a passenger car ignition curve was more like the analog boyer and a performance car (with the same engine) ignition curve was like the points/AAU. Current performance engine building practice remains the same for engines as it was then - all advance in by 3-3.5k RPM.

So that is all I would be looking for in an ignition system for one of these bikes. For racing, curves like the analog boyer are fine because you are never down in the rev range where the reduced advance occurs. Assuming the timing is set for the same maximum advance, there is no difference in maximum power for any of the ignitions; it's just a matter of better midrange response if you get the advance in earlier. The advantage of an ignition that doen't get the advance in early is that it is less prone to detonation with poor fuel. Perhaps that's a design choice of some of the makers; but the tradeoff is reduced low/midrange power.

FWIW years ago I had points ignition on my race Atlas , fixed, no AAU. Set to 28 degrees and I could push start it in 3 steps, and it was the quickest bike off the line at Brands Hatch.....and that was in a mixed capacity grid...even starting from cold was easy....yes, the fixed ignition made it quick off the line and out of corners, but it didn't affect an 800rpm tickover and easy starting! (ok, I never had to kickstart it, but you can tell how easy a bike is to start even from a push!)

I run a MD Power unit on my 850 and it fried the micro coil not long after I bought it which Boyer replaced quickly. They said it was the first ever to fail.

Performance and starting is good while tick-over very stable. I've found my Commando runs better and cooler with 28 to 29 degrees fully advanced (9.5:1 3s cam etc) I do agree that there's some poor petrol about. I filled up with Esso 97 oct just before my wife and I set off for Holland, starting became difficult and a vibration above 3000 rpm could be felt through the bars. You bet I thought the Boyer was going to let go, but a fresh tank full of petrol fixed that.

Has anyone else noticed how bad some petrol smells, akin to rotting flesh or somethin'

Cash

Hi did someone had any new curves ....? should be nice to have the Old Brits one, Smart Fire, and Saches!!

marinatlas said:

Hi did someone had any new curves ....? should be nice to have the Old Brits one, Smart Fire, and Saches!!

Click to expand...

and the Pazon Altair, which from the graphic on the Pazon site looks similar to the Trispark and is all in by 3000 rpm.

Using Pazon Altair here and very happy with performance. Has the idle stabilization and idle is stable as a rock. Priced between Surefire and Smartfire - about $250.

Russ

+1 on Russ's comments

Richard

Just curious... what's the deal with the Boyer from 0 to 1200 rpm?

This all only goes to prove how variable our old nails are. My 850 was fitted with a Boyer for ten years. It always started first or second kick, never kicked back & ran very well. The one exception was, it had a very unreliable idle. I always put this down to carbs. After reading a post on this forum decided to fit a Trispark. Instant idle was the result.
A while later I fitted one to my '68 750 but this didn't respond half as well.

Martyn.

The unpredictable idle was part of the norm, therefore the revving at stoplights to reduce the inconvenience of stalling. A skill the Village People impersonators have perfected to an art form with modern fuel injected cruiser sporting open pipes. :lol:

David Comeau's advance curve for the Lucas RITA shows distributor rpm and Distributor degrees. Is that half of crank rpm and advance degrees?

illf8ed said:

David Comeau's advance curve for the Lucas RITA shows distributor rpm and Distributor degrees. Is that half of crank rpm and advance degrees?

Click to expand...

Yes.

Interesting and timely for me that this thread popped up again.

Since my post here is nearly 3 years old, I'm re-posting a more recent graph that includes Pazon's Altair EI (apologies to Boyer fans, but I needed to drop a few curves for clarity).



What has been missing is a standard PowerArc curve provided by Old Britts. If anyone using this system could post that curve, I'd be happy to superimpose it on to the graph above.

Conventional EIs like TriSpark and Pazon are simple systems, producing a single pulse on every compression or exhaust stroke (there are two sensors 180 degrees apart wired in series). These systems work happily in an rfi environment limited by 5 kOhms of damping in the HV circuit. PowerArc is a different animal, dealing with a string of 45 pulses per crank rotation, and is much more sensitive to rfi. As a result, PowerArc requires twice the damping, a total of 10 kOhms, in the HV circuits, which reduces the peak current and discharge duration (it's a simple L/R decay) to half of that obtained in conventional EI systems. To compensate, PowerArc fires on three consecutive pulses, extending the effective pulse duration to 2.6 ms at 1000 rpm. While this recovers the pulse width reduced by the 10 kOhm damping, it does not recover the lost peak current. The clever trick of triple-firing (my hat's off to the design team) compensates for the reduced spark duration, but provides no other benefit, other than in marketing. For those on this board who have come to appreciate idle-stabilized advance curves, this feature is still missing in the few PowerArc curves that I've seen. I really can't see how triple-firing can produce a more stable tick-over than any conventional EI with 5 kOhm damping.

I can't see how any of the curves shown above (other than the AAU) are amenable to idle stabilization in the range of rpm where idle should occur the curves are relatively steep so a bit of hunting for advance at idle. The AAU curve is flat. I have seen sticking AAU's as a very common culprit in high or fluctuating idles but that is due to wear or lack of proper maintenance of the AAU causing them to hang.

Triple spark duration of 2.6ms duration reminds me of three stirkes and you are out. If it does not ignite by the first spark, what's the point of firing again. If it ignites on the first spark, then I would think the second and third firing would be in the falme kernel and wonder what the point of that would be. I see the analogy of committing to staring a fire with three matches; after the first match starts a blazing flame, one continues with the second match and the third match.

This sounds a bit like a design compromise in the functionality which I see is getting the mixture lit ASAP. I see no advantage in three pulses as opposed to one good spark of adequate duration. My comments are based on some recent reading on the subject.

I am by no means an IC engine ignition guru and remain open to learn the wisdom of this design.

Hi , is there any problem running Power arc , while using a Scitsu tachometer , due to those three sparks ?? Yes more feedback, will be welcome, we know Holmeslice use them and is quite happy with, so ...........