Electronic ignition improvement for the Honda XL250.



Like most classic points, condenser and coil ignition systems, the points are prone to becoming pitted because of the amount of current that is passed between the two contact faces of the points. Pitted points are unreliable, as the surface area of the contact is reduced. Pitted points often point to a condenser (another name for a capacitor) that needs replacing.

One solution is to reduce the current that the coils pass in order to trigger a spark from the coil.

Most modern ignition systems are now 'solid state' and points are a thing of the past. Older bikes are few and manufacturers don't cater for a very small market for such machines, so generally if you want to improve your ignition you have to do it yourself.


Mark Temmes from Germany built himself a suitable unit, and here is his email to me:


"After some problems with the ignition coil (or maybe it was the capacitor) I detected too much firing at the contact breaker points.
Even after exchanging the coil (according your advice), there was still much firing in my opinion. It's this firing that leads to wearing.
My old Guzzi also uses contact breaker points, but I unburdened them by a simple (transistor) control joining up in circuit.

It's running with the same set of breaker points for 25 years now. You only have to put some grease on it. [the cam that is]
Such a control is very easy for a conventional coil ignition. But the Honda uses a magneto ignition.
So, I took some measurements and finally designed a simple transistor circuit that runs with this magneto.
It's still triggered by the contact breaker points, but the current through the breaker itself can be neglected.) ['is negligable']
This was some 5 weeks ago, and it's still running fine.
So I thought, I could tell you.
Maybe you find this is a good idea, too.
Maybe you think this could be of note for others.
You know, I'm doing this stuff just for fun (no pecuniary interest or anything).
So, if you would like to put this stuff somewhere on your XL page, I would very appreciative.
I guess, your XL-page has become a real good authority for XL owners all over the world.


Please find attached* some pictures, schematics and the BOM.
Also, there's no need to make any changes in the original harness. So, if it should fail, you can simply switch back to the old circuitry.
Even Ground and Battery (+6V) can be very smart connected at the flasher relay.

R1, R4, R7 = 10kOhm, 1/8W
R2, R3 = 1kOhm, 1/8W
R5 = 200Ohm, 1/8W
R6 = 500Ohm, 1/8W
C1 = Capacitor (300...3000µF, 25V) i.e. 2700µF
N1 = Optocoupler z.B. SFH610A-3
Z1, Z2, Z3 = Zener-Diode 15V, 0.5W
V1 = Transistor pnp-Darlington i.e. BD680
V2 = MOSFET p-channel, IXYS Typ IXTP10P50P
V3 = MOSFET n-channel, IXYS Typ IXFH44N50P
V4 = Diode (Ur>100V) i.e. 1N4004...1N4007
V5 = Diode (Ur>400V) i.e. 1N4006, 1N4007
V6 = Schottky Diode (Uf<0.5V, If>10A) i.e. S30SC4M
The range of suitable parts indicated with "i.e." is very wide.
I just took these ones, because I found them in my shelf.
Any other parts with roughly similar properties will also do.
V3 and V6 are burdened (take care with cross section of the conducting path).
V2, V3 and V5 must withstand the generator voltage in the moment of ignition (approx. 130V peak).
I choose parts >500V. I can't stand if a system is always tight dimensioned ;-)"

* Mark's attachments are below:-



Well I hope this has been of interest. Thank you to Mark for letting me put this useful information on my website. If you need to contact Mark, email me and I will forward it to him.

Happy riding!