Electronic Ignition Questions

[Mark A]

Can anyone explain in technical detail how magnetic systems like Pazon/Rita achieve advance/retard? Apparently they do so by magnetic thather than electronic  means which I don't understand.

Also, anyone with experience of Runtronic ignition (magnetic) or Accuspark which has programmable electronic advance curves? (are there any others that do this?)

Reason for asking is I have a Sunbeam S7 (well, it's nearly a BSA!) that needs electronic ignition and there is no kit made for it or that will easily fit. Retaining the points and using electronic advance seems to be the way forward. Any ideas/opinions?

And while I'm at it - anyone able to advise on either the total advance angle or even better the curve of a soft-tuned 500 twin like an early A7?

[Spaceman]

As far as I understand them, these electronic ignition systems use a magnetic trigger but control the ignition advance electronically. In principle, I am sure with a bit of electronic skill, it would not be that hard to trigger an electronic ignition module via the old contact breaker unit but that would tend to defeat the purpose for having it!

[Mark A]

I thought that too but it isn't the case. Somehow the magnetic pickup does it  - but how?
Not much wrong with points, they last ofrever if the current is kept  low as with electronic discharge systems and they're super reliable. Its the clunky old mechanical advance retard that causes most ignition problems.

[DAVE BRADY]

Hi,

Have a look at this.

http://www.sunbeam-twins.com/completed-engine-speed-ignition-sytem.html

Dave.

[Mark A]

Thanks Dave, I know...sadly the fella doesn't answer his phone or return messages so I think it's ancient history. Otherwise it looks like a neat installation. I suspect it's a one-off and not marketed though.

[Spaceman]

I thought that too but it isn't the case. Somehow the magnetic pickup does it  - but how?
Not much wrong with points, they last ofrever if the current is kept  low as with electronic discharge systems and they're super reliable. Its the clunky old mechanical advance retard that causes most ignition problems.

Both the Pazon and Rita electronic ignition systems mentioned use electronic advance and retard. All the magnetic pickup does is generate the trigger signal.

[DAVE BRADY]

Hi,

I think Kirby Rowbotham, mentioned in the article, is still trading so may be able to help.

Dave.

[Mark A]

Spaceman, I am pretty certain that is not the case. I believe Rita, and I know Pazon (because they have told me) do not control a/r with the electronics box. (Pazon  said that I needed to retain the points and a/r unit ergo their box does not have this ability). That function is somehow a feature provided by the magnetic operation of the pickup system. (yet Pazon is a magnetic system - I don't understand!) A vague memory of 6th from physics suggest this may be related to a property called 'reluctance' but I stand to be shot down over that.
My research suggests (from Runtronic's advice pages which are considerably more technically explicit than most) that  setting the trigger coil at different angles to the plane of rotation of the magnet/s varies the advance. Quite how and how one predicts this I have no idea and they're very vague on that aspect. I'm pretty certain all the other magnetic trigger systems are the same inc. Rita.
The only system that I've found that clearly states  it controls the advance curve by solid-state means (as opposed to magnetic)  is Accuspark and their curves are  allegedly fully programmable, a claim I've not encountered anywhere else. They are, however, rather vague on the nature of the 'trigger' system...

Kirby Rowbotham's website does not work and I've not had a reply to messages left on his phone so I suspect he is no longer functioning - but I'd love to hear differently as he seems to be  the only one to have had a proper go at solving the S7/8 problem.

Please, there are a lot of Sunbeam owners out there who'd love to have a decent ignition system that isn't subject to the random vagaries of an utterly defunct Joe Lucas 1940's distributor and floppy bobweights on worn out and rather arbitary springs...

Keep the info coming!

[DAVE BRADY]

Hi,

Is this of any help.

http://www.sunbeam-twins.com/redundant-spark-ignition.html

Dave.

[chaz]

I was running electronic Wassell on the B40, no bob weights involved, the A10 has an old electronic system, no bob weights and the A50 has electronic waiting to be rebuilt and also has no bob weights its an American import system came with the bike. In all cases the A/R is handled by the electronics unit.

[Spaceman]

Spaceman, I am pretty certain that is not the case. I believe Rita, and I know Pazon (because they have told me) do not control a/r with the electronics box. (Pazon  said that I needed to retain the points and a/r unit ergo their box does not have this ability). That function is somehow a feature provided by the magnetic operation of the pickup system. (yet Pazon is a magnetic system - I don't understand!) A vague memory of 6th from physics suggest this may be related to a property called 'reluctance' but I stand to be shot down over that.

The Boyer-Bransden MkIII elecxtronic ignition system certainly uses electronic advance/retard within the ignition module. It's incredibly hard to find a clear description of how the Pazon Sure Fire system works but the link below indicates the ignition advance/retard is carried out within the ignition module. In both cases, the ignition module is triggered by a magnetic rotor or reluctor and a pickup coil.

https://www.pazon.com/ignition-system/surefire-module-12v.html

[EDDIE SIMPSON]

electronic ignition only alters retard up to about 3 to 4000rpm , thats why you strobe to 5,000 rpm with rita and set full advance. very simple really . if you have used a manual magneto before then the rita box saves working the cable lever.

[Spaceman]

Having looked into this, I see that Pazon now do the analogue Sure Fire electronic ignition but they also do the digital Altair system. As far as I can see, compared with the old mechanical AR mechanism which gives full advance by about 3,000 rpm, the analogue system gives full advance only by about 5,000 rpm. Potentially, this could result in less mid-range power. The advantage of the Altair system seems to be, among other things, that you can program the AR curve to tailor it to your specific requirements - a bit like re-mapping on modern bikes.

[Mark A]

As ever the system would work except for the same old thing - the design of the Sunbeam distributor  prevents the fitting of pickup plates or the rotor itself due to the distributor shaft having a top bearing in a cast housing above the points cam.
This virtually compels the continued use of the points (which I don't mind) but does requir the electronics box to work witth 12v switched by points. So far the only one I've found that does this is  Accuspark. There's no indication that Altair can do so as it is pictured with a magnetic pickup and rotor.

[Spaceman]

In principle, it would be very simple to reduce a points switched 12 V down to the voltage level output from a magnetic pickup - it just requires two resistors, assuming this polarity is required by the ignition module. I've got an old Boyer Bransden in my shed that should work in the same was as the Pazon Sure Fire - I'll see if I can test it to work out what magnetic pickup voltage it normally produces and, if the ignition module still works, I'll test it with a 12 V derived input.