CB650 charging issue

 I need advice from someone knowledgeable re: bike electrics -- if you have
to guess, I appreciate the help but I have a question whose answer may leave
no room for error.

I got a creamer 1979 Honda CB650 with exceptionally low mileage for a steal
because a guy died and left it to his middle-aged non-biking sister. It has
the charging problems typical to those bikes. I have researched the issue
online, gotten hold of the protocols of diagnoses, and read, read, read,
about it.

I was able to do the simplest diagnostic tests such as checking, with a new
fully-charged battery, to see if the voltage increased when revving to the
given 5000 rpm. There is nothing there but the battery voltage, and if I
drive it awhile the voltage drops significantly toward dead and will
eventually kill even the engine. I don't need any more evidence that the
charging system is kaput. Further, I meticulously cleaned every connector,
even though they were all already clean and uncorroded, and it made no
difference. I have no access to a shop, and no desire to do any of the many
more technical tests -- would rather simply install new parts.

I intend to replace the regulator/rectifier (one component) and/or the
rotor. I read from an expert who says the stator is the least likely to go,
and if it does it is usually a case of some things burning up, of which
there is no obvious hint so it seems like that should be the last thing to
consider. I know that, in the case of car electrics, it can matter which
components you replace first inasmuch as if you do it in the wrong order a
bad component can cause the replacement of another part to fail. I am
wondering if any similar conditions pertain to CB650s since I would
naturally like to replace the parts starting with the least expensive.

So, what is best -- replace the rectifier/regulator first and if that
doesn't solve the problem go ahead and replace the rotor too? Or the other
way around?

Thanks in advance,

pflu

 Phluge wrote:

Wait a couple of days to see if an expert or two here gives some cogent
advice!


I'm not one of them, but from what little I know, would think if you can
check battery voltage, it won't take more than a couple of minutes to
check stator output (eg., you may have to remove the seat).  That might
certainly help to isolate things to a useful degree.   Could save quite
a few bucks plus lots of wasted time obtaining parts one by one.

 
, would think if you can

Can you elaborate -- how do I check the stator output? Is that the one where
you measure the voltage across the battery with the engine at fast idle?

pflu

 Phluge wrote:
...

If I've got it right, that one tests the whole charging system (except
for the battery), not the stator/alternator output by itself.  I found a
wiring diagram at

http://cosky1.tripod.com/index.html


under the seat there will be a multi-wire connector that joins the
alternator to the reg/rect and probably three of those wires will be
yellow in colour (plus two more, one black and one white).  You can
check the yellow ones in pairs, eg., uncouple the connector then check
each yellow to one of the other yellows, with the meter set to AC
voltage - if the alternator is working fairly well, on each of the three
pairs you should see much more than 12 VAC, perhaps as much as 30 or 40
VAC when you have the engine revving fast, say 4000 or 5000 or more.
That would tell you there is good chance there is nothing wrong with the
alternator.


I see there is another post from "." about testing the reg/rect itself
with battery which would help point the finger at that part if it is bad.


As I said, I'm not an expert, my electrical trouble-shooting skills are
  so amateur that nearly always I have to refer to an online source or
an  electrical troubleshooting book, but not always the factory service
manual (it seems some of the typical resistance tests in factory manuals
aren't always helpful because while they may tell you a part is bad,
they don't assure you the part is good).


Not telling you what to do, bu a couple of sources I know of, eg. on the
www are:


http://www.motorcycleproject.com/   gives some tips, one I like is how to
make a high current shunt.


Some shortish books that I know of are


"motorcycle electrics without pain" by Mike Arman

"motorcycle electrical systems" by Tracy Martin

 Oh, here's another link to a nice simple guide that one of the regulars
here mentioned a few weeks ago:

http://www.electrosport.com/technical-resources/library/diagnosis/pdf/fault-finding-diagram.pdf