QuestionI have a 85 Yamaha virago 1000,back cylinder does not fire.Plug will fire outside of cylinder.If it is running and you pull the plug wire on frount cylinder it dies.With running pull back wire nothing happens it will stay running.With plug out of back on the head it has nice spark,when i first pull the plug it ie wet so i think it is getting gas and fire.I tryed new plug's still the same.plese help,thank you for your time
AnswerHi Newt,
The Virago often suffers from excessive resistance
in the electrical circuits.
The connectors that join the regulator to the
stator and the other connectors that it
uses on the TCI or transistor controlled ignition
module etc start to corrode over time and
this is a major cause of cylinder misfires.
If your spark looks steady and strong you
may also want to make sure the rear cylinders
compression is equal to the front cylinders
pressure. Low compression could also cause
a misfire and could be due to insufficient
valve clearance or wear.
To properly clean the electrical connections
you must use electrical cleaner like "DeOxit"
or something made specifically for electronics.
Do not use wd40 or such as they do not have
the correct properties to remove the corrosion.
Spray the connectors and work the connectors
in and out a few times to help clean them.
You can do all the connectors you can find
on the bike, especially those for the
ignition and charging components.
Next, clean the battery terminals and cables.
Check the ground cables frame connections.
You may be able to file or sandpaper the
frame for better contact.
Have your battery load tested and charged
up fully as the Viragos respond to better
voltage and electrical power.
If the battery is weak you may often have
a cylinder acting up.
Use some new spark plug caps as the originals
have high resistance and can fail.
Many people have been able to rectify the
rear cylinder problem just by getting all
the connectors cleaned up this way.
Of course a plugged idle jet or passageway
can cause a similar problem so dipping the
carb in Yamaha carb cleaner can help there
or run some "Seafoam" fuel treatment through it.
The last course if your compression is good
might be to try another transistor module
on it. The solder joints can go bad after many
years and cause some erratic symptoms.
The high resistance in the connector plugs
can also affect the module so carefully
cleaning all these connections may solve
the problem if it is electrical.
http://www.jetav8r.com/Vision/TCIRebuild/TCI_Rebuild.html
If the fuel flow is good and the compression is
good then another thing to check on these
is the carb mounting rubbers which can develop
hair line cracks underneath. These cracks
allow the engine to pull air into the intake
tube which results in a lean fuel mixture
to the cylinder which will not fire properly.
Either replace the carb mounting tubes or check them
carefully for cracks. You might even coat
them with a layer of silicone rubber or such
to prevent any air getting into the engine
without going through the carbs first.
Any air or vaccuum leak around the carb mounts
will cause a too lean fuel situation.
I think the problem is likely an air leak
or high electrical resistance so look for
those things first.
Good luck!
Wayne S.
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