Motorcycle Repair: sparking units, honda cb750, electrical units

Question
QUESTION: Hi Rich,
I have a honda cb750 f (81) The two electrical units under the seat Part # mps200 seem to be melting the waterproofing off.(it looks like tar)before I buy new ones is there something causing this or are they just worn out? They are pretty expensive so I want to make sure. I have heard them being called" sparking units" Thanks so much for your time.

ANSWER: Are they still working?  Those units are potted and it would take a lot of heat to melt the potting.  If they are getting hot enough to melt, I wouldn't think they would still be working.  So it makes me wonder is that's what's happening.


Regards
Rich

---------- FOLLOW-UP ----------

QUESTION: Hi rich, the bike still runs fine with those units, the wires are intact but all the "potting is melted away" I'm sure it's just a matter of time before they fail. My question is do they fail on their own or is another electrical component adding to their failing.I don't want to buy new ones until i figure out what's causing it to happen.  Thanks for your time.


Answer
Doug, I've never seen the potting melt out so I'm not sure what to tell you.  There shouldn't be a lot of current in those boxes since they only switch the ground on and off to the coils.  It could be high resistance in the connections or high voltage output from the alternator.  Take a close look at the connections out of the alternator and see if they are melting.  I'm not sure how that could increase the voltage but it a common problem and caused my neighbors bike to catch fire.  So I'm wondering if something like that could be increasing the resistance or voltage in that circuit.

Regards
Rich