From: mitch@seashell.seas.ucla.edu (Robert R. Mitchell (SEAS admin))
Newsgroups: rec.motorcycles
Subject: Help! Electrical problem w/Shadow
Date: 28 Jul 92 18:00:00 GMT
Organization: SEASnet, University of California, Los Angeles


HELP! My 87 Honda 700 Shadow died; some sort of electrical problem.
Maybe this will sound familiar to someone out there:

I had just been for a short ride (45 mins) in 105-degree heat.
I had just exited the freeway, went about a block, everthing normal.
Made a left turn, bike starts bucking and trying to stall, even
backfired once, low fuel indicator lamp was flashing, and the tach
needle was swinging wildly from zero to redline.  I managed to 
coax it another few blocks to my driveway, and shut it down.

A few minutes later, when I turned the key to ON, it was completely
dead: no indicator lamps at all, and of course the started won't 
spin (the starter relay doesn't even "click").  

Things that check out okay:

    o  wiring and fuses (not 100% certain about wiring)
    o  l/r handlebar switches
    o  regulator/rectifier
    o  alternator
    o  coils (difficult to check, but seem okay)
    o  neutral switch, oil pressure switch
    o  clutch diode

Things that seem questionable:

    o  overdrive indicator switch (no cont. w/ ground, but ???)
    o  battery
    o  spark unit

Okay, the battery was toast.  It did have voltage (although low) when 
measured without a load, but with a load (trouble light) the voltage
dropped even lower ( < 5v).  I topped off the cells with distilled
water and put it on the charger.  I'm not sure if it is going to
hold a charge; the specific gravity is getting better, but the no-load
voltage so far hasn't gone above about 11.5v.

I am using a known good, fully charged battery in the meantime while
diagnosing the problem.  With the good battery, the indicator lamps,
taillight, and headlight now work when the key is ON, the starter
relay "clicks" audibly, but the starter won't spin.

I've described the symptoms to two service managers at different
shops, and the instant I mentioned the wildly swinging tach needle,
they said "sparkbox" (meaning the CDI spark unit).  There is no
way to check out this unit.  Shop manual says if all the related
components are okay, and the bike doesn't run, it's gotta be the
sparkbox.  It's expensive (>$125), and probably a special order
part that can't be returned, so I want to be certain about that
being the problem.

The possibilities are:

    o The sparkbox died, and took the battery with it
    o The weak battery killed the sparkbox somehow
    o The sparkbox died, weak battery unrelated
    o Extreme heat killed sparkbox and/or weakened the battery
    o I've missed something

I'm puzzled why the starter motor won't turn over.  There is
a wire running from the sparkbox to the starter relay, so
I guess it could be related.  I'll check that out further
but "bad spark unit" isn't listed as one of the causes under
the "starter motor won't turn" troubleshooting section.

So, has anyone had any experience with a bad spark unit,
and do these symptoms sound consistent with that failure mode?

Any suggestions or encouragement will be much appreciated!


--
DISCLAIMER:                                              | Bob Mitchell
"Don't blame _me_, _I_ didn't do it!" --Krusty the Clown | mitch@ea.ucla.edu
"Ididn'tdoitnobodysawmeyoucan'tproveanything!" --Bartman | DOD#[classified]
"Computers are ruining this country." --Al Bundy         | 1987 VT700c
Newsgroups: rec.motorcycles