Hi Luis, The primary is likely to be quite low resistance anyway and therefore may be OK after all. If both ends of the winding are available, check it hasn't got a short to or earth/frame etc. This is somewhat more likely than shorted turns, although this is possible. Is their a mechanical switch, or is the operation electronic? If electronic, it can be possible to switch the electronic parts for a generic switch unit. It's just a matter of finding something suitable ----. Capacitor failure is also not unknown and the problem is that it breaks down under high voltage so looks OK when tested. Replacement is generally the best test for them. If you can borrow parts from a similar unit you should be able to isolate the problem. Magnetos work by interrupting the current in a short-ciruited coil (the primary) which induces a much higher voltage in an overwind (the secondary). The switching used to be a mechanical switch, but these days is usually electronic and triggered by measuring some variation in the coil current as the magnet passes. Or by separate sensor in some cases. The capacitor provides a bit of control over the resonant frequency which effects maximum voltage and spark duration. RP On 26 November 2012 09:49, Luis Moreira wr= ote: > parts: ignition coil, > some sort of pickup and the magneto/cap part that > --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .