Member Article - Misfire 1000 Virago

Below is a member sunmitted article. Many thanks to Tom for submitting to the site his experience in troubleshooting his Yamaha Virago 1000.




First off, thank you for the great tool you guys have built in collecting
all this information and making it available to the likes of myself.  I
have been on your website a great deal over the last few weeks as I
recently purchased a pair of 84 Virago 1000's as some "projects".  I
recently developed a misfire and the symptoms were listed on your website
but I thought that I'd share my findings with you as it appears that my
symptoms were similar but the problem was different!

I was having issues with my bike developing a severe misfire shortly after
I started it up.  It ran good for the first few seconds and then it seemed
my rear (#2) cylinder would just start periodically missing.  In addition
to the misfire (and a lot of backfiring) I would loose my tachometer at the
same time.  After disconnecting the tach, replacing coils, replacing the
TCI (I have two bikes, so no big deal swapping parts back and forth!), I
started looking much closer at timing.  I put a timing light on each plug
and noticed that the timing became very irregular once I started to rev up
past idle and along came the misfiring.  I'd had trouble with the boost
sensor and swapped that out (again) and had the same results.  I then
started to dig a little deeper.  I started to be suspect of the voltage
regulator/rectifier and checked AC input voltage and frequency and all
appeared good.  Output voltage however, was very high - 18VDC.  I
disconnected the regulator/rectifier and just ran directly off the battery
and instantly the bike ran beautiful!!  In the end, I swapped
regulator/rectifiers with the other bike and that's all it was!

Long story short, if people are getting all the symptoms of a bad coil, or
a short on their primary winding side (tach dropping out), it could be an
overvoltage condition and to check their regulator/rectifier!!  I suspect
the TCI was doing wonky things as a result of an over voltage condition,
and I also suspect that my TCI will be the next thing that fails as I've
probably nearly destroyed it by pumping irregularly high voltage into it.

Thanks and hopefully my troubleshooting will help someone else out!


Copyright 2016

Date Submitted July 31, 2016

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