Understanding a Honda CRs Electrics

[Kenneth S (222)]

Hi Guys,
I have read a few times about the benefits of having the Stator Coils rewound, more recently by lukeb1961 on this thread http://ozvmx.com/community/index.php?topic=23039.0

I have a few questions.

Is it only the stator coils which require rewinding to give you a strong spark?

What about the ignition coil, does that require rewinding, if that is possible, or at least replacing, at the same time?

If you are going to take the step of having the stator coils rewound, shouldn't you have the magnets recharged at the same time?

On the attached photo are the primary and secondary coils the 2 marked as A or are the 2 marked as A the primary coil(s) and the one marked as B, the ignition coil, the secondary?

[Montynut]

Hi Kenneth,
Well here goes if I have left somthing out or off the mark then someone please correct me

The Ignition coil 'B' contains both a primary and secondary coil. The secondary has a very high number of turns compared to its primary. This acts as a simple transformer energised by the primary coils magnetic flux rapidly collapsing when the ignition 'firers'

The box contains the capacitor and electronic circuit which charges a capacitor and rapidly discharges it through the ignition coil 'B' primary. There is also often some form of advance retard built into the electronic circuit although this was not very advanced in the ‘70s. This advance/ retard is separate to the small amount of ‘natural’ advance/retard gained from the speed changes of the engines flywheel and its magnetic flux rate of cutting.

The stator coils ‘A’ have two jobs. One coil generates an AC supply to power the whole system while the other coil acts as a trigger to ‘time’ the spark or more correctly the datum point to ‘fire or trigger’ the electronic circuit. The arrangement and role of these coil changes from system to system but all basically follow that principle. When lighting coils are included it complicates things as usually on dirt bikes they are completely separate electrically.

Most of these system are very basic compared to modern programmable systems but I am a big fan of the ‘KISS’ principle. When you send your stator for a rewind at either Small Coil Rewinds in VIC or Betta Bikes in SA they need the whole system and will do a complete check and if the flywheel needs remagnetising then it will be done along with rewinding etc. Rewinding the coils sounds simple but the knowledge and experience these guys have is invaluable and the cost is (in my opinion) well worth it.

Make sure you thoroughly check the earth system on your bikes as this is an area that is often underestimated in its importance for the overall performance of the system. One poor earth and even the best ignition system will give weak spark. I mean all connections not just the connectors on the wiring ie contact between stator plate and engine casing, ignition coil and frame and importantly frame to engine casing.

[Lozza]

That's a great overview of the high voltage system(AC) these days we use DC/DC which have a external magnetic pick up and a ferrous trigger bar breaking the flux. Why DC ? Simply they push more voltage to the plug the max advance is built into the trigger bar.
The CDI only has to retard.

[Montynut]

Yes the modern systems use a much different system which lends itself to much more advanced (complete freedom really) tuning regarding maps etc. The old systems also used DC to the capacitor and ignition coil as they would not work otherwise. The first component within the CDI box or electronics is usually a diode giving 1/2 wave rectification (and therefore only using half the available energy ) or the rectification is achieved via the transistor / SCR combination which fires the system.

These older system are considered to have static timing for all intensive purposed although do retard at high rpm I believe and naturally advance again when rpm is reduced. They also have a small amount of natural advance caused by the trigger coil being excited earlier in the revolution of the flywheel because as rpm increase the rate of change of magnetic flux acting on that coil increases at the square of the speed change (from memory?). This change in timing is not great and usually as far as I understand is not considered in tuning.

The other big advantage of the modern systems that Lozza describes with the separate trigger devices is dead accurate timing every revolution every time while the old systems are no where near as stable regards to timing. I am not up on the advance retard mysteries of the engine tuning world but more familiar with the electrical components and there function.

Lozza do the new systems push higher voltage or much higher energy hence the lovely big fat blue spark? I think that its much higher energy more than just higher voltage although I am sure the voltage is also higher but the old CDI systems voltages are fairly high as well. I would guess that the available joules of energy available at the spark plug would be double or even tripple that of the old systems from the 70's and 80's

[Hoony]

Good Explanation Montynut, you are obviously a sparky or in the electrical/electronic industry !

[Lozza]

It's higher energy(higher voltage is easier to understand). It has to do with the windings on the stator the DC stator more turns or thicker wire diameter whatever it is that allows higher voltage off the stator with the same space available.Nothing is lost in the conversion from AC to DC. Better and more sophisticated electronics require stable DC voltages.
Latest ignition I use can make a spark jump a 20 odd mm air gap

[Kenneth S (222)]

Thanks Monty and others, that helps me have a better understanding and has highlighted some maintenance I must do.

By the sounds of it, the bottom line is this. If my goal is to have the bike running to it's full potential, it seems I don't want to be putting the cart before the horse power (bad pun intended) and playing with the jetting until I know what I am beginning with is a solid foundation, being a strong, reliable spark.

So, before I do anything else, I should ensure the electrical system is running as it should. Therefore, when I do make jetting changes, I am getting a true indication of how they effect a properly running motor.

It certainly won't hurt to do as Monty has suggested and in addition to checking the earth connections, the plug cap and the plug, send the whole system to one of the engine rewinders listed first and have it checked.