SOHC.co.uk Forums > CB750
Aftermarket Coils
Bryanj:
Not necessarily maybe only 1 set of points were closed
AshimotoK0:
Probably a low resistance coil design. It's all about Amp/Turns .. they probably reduced the number of turns of the coil to decrease resistance in order to save the cost of copper but still get the same magnetic flux. Unfortunately, that vastly reduces the 'duty-cycle' ... meaning if you leave the coil energised for a long period it is likely to suffer burnt out windings. Never really seen that happen on a genuine Nippon Denso coil (typical DC resistance of a Denso coil is typically around 4.5 ohms). It's different with a CDi system coil as they can be low resistance and low duty cycle because they can never experience long term continuous current flow in normal use or when the engine is static but the ignition is switched on.
Moorey:
--- Quote from: Bryanj on March 25, 2020, 08:51:14 PM ---Not necessarily maybe only 1 set of points were closed
--- End quote ---
Quite true.
philward:
All very interesting - I've emailed M&P for a relacement. Will be careful in short term and recon a std set as per James method before I sell the bike
gtmdriver:
Make sure that the coils have the same primary resistance as the originals. (3 -4 ohm).
Coils designed for use with electronic ignition systems have a very low resistance (1.5 ohm) so when the points are shut twice the current will be flowing through the system. I'm not saying that was the reason for your failure but if you fit the wrong coils the points will burn very quickly and you could damage the condensers.
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