Just sorting out the electrics on my mid-80's 650 project bike. The CDI units are standard Bosch 1 217 280 034 units. The coils are Tec MP06. The wiring diagrams and parts lists refer to resistors between the CDI units and the coils. Other posts in this forum refer to 0.99 ohm resistors. Do these coils need resistors, or was that just for the Bosch coils which I think were used in very early systems? On the coils, one terminal is green and the other black - anyone know which is the power feed and which the trigger feed? Or doesn't it matter? The electrics are a real mess on this bike so anything is possible!
Sorry. I don't know if the MP06 coils need resistors. With regard to the polarity, if you have it the wrong way round the spark will jump from the body to the electrode instead of the other way round. This would probably be ok and you might never notice but the spark will jump easier from a fine point than the blunt surface.
do you have an multimeter? On the terminals of the primary coil (the bit the spade connectors go on) you can test to see the resistance. It doesn't matter which side the connectors go on to as you're energising the coil. What plugs are specified for the bike as some plugs have a resistive cap in them as standard. it may be that the CDI unit of the time was incapable of working with short dwell times on the coils, thus the resistor was there to stack up and create a longer dwell. 3 ohm was common for many ignition systems both Japanese and Italian at the time. You need to find out what the resistance of the coil is and what the resistor inline is. The longer the dwell, the more chance that current in the primary coil will have reached its maximum value. The trade off is that the longer the dwell time used the hotter the coil will run, and the shorter the life of your coils is likely to be. Always a good idea to reposition them in the airstream if you can.
The early systems did not use Bosch coils, but Nippon Denso coils number 129700 (80 mm bolt spacing) as per this photo: The resistors were Bosch number 0 227 900 002. In the workshop manual, the resistance value is given as 0.9 Ohms.
Thanks - that's really useful info. I am planning to replace the Bosch CDI units with a twin-circuit Horse Power Ignition one (https://www.hpi.be/item.php?item=CD6905D) which should drive the coils fully without the need for resistors - but I had better check with HPI first. Has anyone had experience of the HPI unit??
Good-looking product - thanks. Pricing looks about the same level as the HPI, and a recommendation is always a good thing!
you'd only need the 2 channel unit not the four, so a connection lead for the ducati loom is 5 euro, the basic harness is 7 if all bought with the unit, which will be 138 euro. You don't need the basic harness but its a nice to have if you ever want to consider remaking a loom or adding bits. The connector pins are the same as sumitomo HM connectors so readily available, and there's lots of support out there for these units on Ducati. You can also get retrofit tps kits for the ducati mikuni carbs.
