Converting your Femsatronic CDI to a Ducati
Here is the original website that explained how to replace the Femsatronic CDI with a Ducati (Horta das Vespa)
| Kristian Storli of Bar Italia Classics clarifies the above website and explains why we delete the blue wire. Green wire from stator to the Red Terminal, Red wire from stator to the Green terminal, Black wire from stator to the White terminal then cap and stow the Blue wire (or remove it and the condenser that it is attached to on the stator side, as the Ducati CDI has its own condenser inside the box). |
Hey guys. I had the pleasure (?) of working on a Rally 200 with a dead Femsatronic ignition lately. I basically replaced everything in the
ignition system piece by piece, and the pickup checked out fine, so it came down to the ignition unit itself. I had a spare P CDI laying
around, so I figured I would give the simple conversion described here a try:
http://www.scooterrescue.com/Femsa2Ducati.html
With the lights off, it worked perfectly, and the previously dead engine fired right up and revved out like it should. Problem solved.
Until you turned the lights on, and then it spluttered and backfired and refused to do anything other than idle irregularly. Turns out,
this is a known problem:
"WARNING: This conversion does not work with all Rally 200's! With some, it works perfectly with excellent results. With others, the
engine will misfire and won't 'rev up' if the lights are on. I don't know why this happens, what is the feature that makes an engine
susceptible to the problem, or how to fix it."
http://clientes.pluricanal.net/pla00523/conversaoi.htm
I dug into this issue a little more and figured out a hack that makes it work-- at least on this one bike.
The problem is that the Ducati CDI is made to trigger off of a hall effect sensor, and the Femsa pickup is a reluctor type pickup
instead. The two kinds of pickups put out completely different signals. I have no idea what circuit is inside the Femsa ignition, but it is
definitely built to work well with the Femsa reluctor pickup in ways that the Ducati CDI is not. Specifically, when you start drawing
power from the lighting coil-- which is adjacent to the pickup on the stator-- the signal from the pickup becomes extremely noisy and
full of lots of peaks and valleys that shouldn't be there. The Ducati CDI does not do a good job of filtering out these spikes (because
why would it) and it ends up firing at all kinds of weird intervals. Bad news.
My fix was to make a passive filter to go between the pickup line and ground. The filter is just a 1kOhm resistor and a 4.7uF capacitor
in parallel. These are connected between the green stator wire and the black stator wire, or, from the CDI point of view, between the
red input and the white input. I made up a little mini-harness to go between the stator wires and the CDI that had these components
soldered into it, but do whatever works (the first version was made with alligator clips and a paper towel).
Don't use a polarized electrolytic capacitor like the ones you'd find at Radio Shack; they'll work in the short term, but they're not
suitable for long term use. You need something bipolar like this one:
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=P1199-ND
This fix is definitely a hack and does not completely turn the reluctor signal into a nice hall effect type signal, but it does get rid of the
noise effect and it makes this particular bike run fine with a Ducati CDI with the headlight on, so it does something right. I'm very
curious to see if it works out for other people with this problem. Let me know what you find out!
Jon Scott
ignition system piece by piece, and the pickup checked out fine, so it came down to the ignition unit itself. I had a spare P CDI laying
around, so I figured I would give the simple conversion described here a try:
http://www.scooterrescue.com/Femsa2Ducati.html
With the lights off, it worked perfectly, and the previously dead engine fired right up and revved out like it should. Problem solved.
Until you turned the lights on, and then it spluttered and backfired and refused to do anything other than idle irregularly. Turns out,
this is a known problem:
"WARNING: This conversion does not work with all Rally 200's! With some, it works perfectly with excellent results. With others, the
engine will misfire and won't 'rev up' if the lights are on. I don't know why this happens, what is the feature that makes an engine
susceptible to the problem, or how to fix it."
http://clientes.pluricanal.net/pla00523/conversaoi.htm
I dug into this issue a little more and figured out a hack that makes it work-- at least on this one bike.
The problem is that the Ducati CDI is made to trigger off of a hall effect sensor, and the Femsa pickup is a reluctor type pickup
instead. The two kinds of pickups put out completely different signals. I have no idea what circuit is inside the Femsa ignition, but it is
definitely built to work well with the Femsa reluctor pickup in ways that the Ducati CDI is not. Specifically, when you start drawing
power from the lighting coil-- which is adjacent to the pickup on the stator-- the signal from the pickup becomes extremely noisy and
full of lots of peaks and valleys that shouldn't be there. The Ducati CDI does not do a good job of filtering out these spikes (because
why would it) and it ends up firing at all kinds of weird intervals. Bad news.
My fix was to make a passive filter to go between the pickup line and ground. The filter is just a 1kOhm resistor and a 4.7uF capacitor
in parallel. These are connected between the green stator wire and the black stator wire, or, from the CDI point of view, between the
red input and the white input. I made up a little mini-harness to go between the stator wires and the CDI that had these components
soldered into it, but do whatever works (the first version was made with alligator clips and a paper towel).
Don't use a polarized electrolytic capacitor like the ones you'd find at Radio Shack; they'll work in the short term, but they're not
suitable for long term use. You need something bipolar like this one:
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=P1199-ND
This fix is definitely a hack and does not completely turn the reluctor signal into a nice hall effect type signal, but it does get rid of the
noise effect and it makes this particular bike run fine with a Ducati CDI with the headlight on, so it does something right. I'm very
curious to see if it works out for other people with this problem. Let me know what you find out!
Jon Scott
This conversion appears to work on many Rally 200s but a few owners have experience problems when you turn your
lights on. Check out what Jon S. did to solve this problem.
lights on. Check out what Jon S. did to solve this problem.
Here is a photo of the 4.7uF
capacitor in parallel with a 1kOhm
resistor, covered in a few layers of
heat shrink tubing for insulation
and durability.
capacitor in parallel with a 1kOhm
resistor, covered in a few layers of
heat shrink tubing for insulation
and durability.
