Motorcycle Repair: yamaha rd350ypvs, regulator rectifier, stroke bikes

Question
hi .i have a C reg ypvs 350lc the unfaired model N i think.i have a charging promblem. when bike ruuning baterry keeps running flat after about two weeks if keep riding.have checked manual,says can be three things, SWITCH,REGULATOR/RECTIFIER,ALTERNATOR WINDING.brought a secondhand regulator. switch is a bit dodgy so orded new one .the main point of question is, is the alternator the same on all models and will a later or earlier one fit into mine model.ihave seen a R version one and guy says it will fit? thxs

Answer
Andrew,
  All the part # information is still readily availible for those years.  A Yamaha parts dept. should be able to check that the part numbers match over the years you're concerned with.  My best guess would be yes.  Be sure though, before you replace the altenantor/stator or have it rewound, that the rectifier (converts AC current the stator puts out to DC to charge the battery) and the Voltage regulator (limiting voltage to 14.5-15 volts to safely charge battery) are performing correctly.  I've had the problem a couple of times on RD 400s and it wasn't the stator.  I'm not saying it's impossible, just the last thing you should test.  Typically an osiliscope is needed to accuratly test a stator for correct readings.  Here's a link to parts for 2 stroke bikes of the era:

motocarrera.com

Hope this helps,
Mike