1st Gen front plug not firing fix (Hopefully)

Steve Munyon stevemunyon at comcast.net
Tue Jun 28 15:07:32 PDT 2011

Short story:
The problem was a weak battery combined with stock Rectifier/Regulator
wiring that needs to be a size or two larger.  Once I made the change, the
weak battery voltage at idle went from 13.1v to 14.2v.

Summary:  keep the #@% battery charged and don’t assume that revving the
piss outta the engine while on the track will charge the battery.

Long story:
I’ve been jotting down the voltage levels as I’ve messing with it.  After
seeing both plugs fire the next day, I made the mistake of charging the
battery overnight.  I should have left it alone until I could duplicate the
original problem.

This forced me into looking for a weak link in the electrical system.  So I
got out the voltage meter and recorded the initial states of battery
condition.   I also checked primary and secondary resistance in the coils,
etc., which were spec. I also put the street lights back on the bike, it
wasn’t too hard, because I had made up some brackets to see what the SV was
like on the street a few years ago.
The battery with the ignition switched off was 12.47v.  Anyway with the
headlight (low beam) as a load, the battery voltage dropped to 11.8v after
5-10 seconds.  So I think the battery is marginal.  I started the bike and
the voltage went to 13.1v.
I checked the primary side of both coils with my scope and I was seeing
400v.  The shop manuals states 150v & up, but a scope is a lot more
responsive the just a peak and hold meter that the factory manual suggests.
To me, that explains the higher peak voltage.

I took the bike for a 20 minute ride and the idle voltage was still 13.1v,
so I revved it to about 5K and the voltage was 13.3v, when I revved the
engine higher the voltage dropped back to 13.1v.  I’ve been searching around
the ‘net for similar problems.  One interesting find, was a bad solder joint
on the signal generator pickup, but my solder joints looked good.  Another
find, was that most Suzuki’s have weak regulator/rectifier based on ‘SCR’s”
while other bikes have an R/R based on ‘MOSFET’s’.  Google them if you’re
interested.  As a band-aid for the weaker R/R the author used 12 gauge wire
with a 30 amp fuse to provide a more substantial current path then the
standard Suzuki wiring which looks like a 14-16 gauge with lots of
connectors.  Whenever I see an electrical connector I always figure on a .1
v drop at each connector.  So I ran a 12 gauge wire from the R/R output
connector directly to the positive battery terminal and took some
measurements.  Key off battery voltage is 12.44;  key on and headlight on
battery voltage is 11.9,  started bike and voltage jumped to 13.6v, after a
minute the idle voltage was up to 14.2v and when rev’d the voltage was 13.8.

Next I removed the jumper wire, went back and cleaned all the connections,
checked the voltage and the voltages were back to where they were before,
low.  At this point, I soldered in the additional 12 gauge wire and the 30
amp fuse ending with a terminal lug so I can screw the lug to the positive
battery terminal.  Checked the battery voltages again and they were back up
to the jumper wire voltage levels and sometimes a little above.  I also
clipped a ½ inch off the spark plug wire just to make sure the connection to
the coil is good.

So that wiring fix combined with a new Yuasa battery I just ordered and I’m
about 95% sure I’ve got the problem fixed.  I thought about going to a
lightweight battery, but after being stranded at the track without a bike I
wanted some old age, proven technology.

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