1st Gen front plug not firing fix (Hopefully)
stevemunyon at comcast.net
Tue Jun 28 15:07:32 PDT 2011
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 dont assume that revving the
piss outta the engine while on the track will charge the battery.
Ive been jotting down the voltage levels as Ive 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
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
wasnt 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. Ive 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 Suzukis have weak regulator/rectifier based on SCRs
while other bikes have an R/R based on MOSFETs. Google them if youre
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 revd 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 Im
about 95% sure Ive 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.
More information about the SV650