Motorcycle Repair: Carbuerators, yamaha virago 1100, rear cylinder

Question
I have a 1986 Yamaha virago 1100, I had to re-jet the carbs after I bought it and it has not run right since. The carb for the front cylinder works fine, good fuel ect, however the carb for the rear cylinder(left side of engine) is not getting ANY fuel at all therefore the bike is running on only one cylinder, any suggestions would help. I had the carbs off again today and I checked the fuel supply line to to the carb and I can blow thru it with the floats down and I can't when the floats are up which is how it is supposed to be so it has to be something in the carb itself because the fuel is there but something is preventing it from filling the fuel bowl and going thru the carb.

PLEASE help riding season is almost over and I haven't put any miles on this year.

Thank you
Jeff

Answer
Hello Jeff,

First make sure the rear cylinder
compression is near equal to
to front cylinder as the engine
uses vacuum to pull the fuel
into the cylinders.

Second, if you can, attach a small
hose to the bottom of the carb
on the drain hole and
open the float bowl drain
screw to check the actual
fuel level inside the float bowl.
There is a picture here:
http://ww2.justanswer.com/uploads/motoforge/2009-11-27_012052_Fuel_level_adjustm

Your fuel level should be very close to
the mating surface of the carb and the
float bowl when full.

If the carb won't fill then it's air vents
or passageways are plugged.
Soak the carb in yamaha carb cleaner.

If your carb bowl is filling properly
and the carbs center needle jet and
main jet are clear, it should be able
to draw fuel into the engine.
If it does not then you may have
a air/vacuum leak somewhere on
the intake tract.

This could be a crack in the carb
intake hose or a vacuum hose
or gasket, anything that allows
air into the intake between the carb
mounting and the engine itself.

You should feel the engine pulling
air into the back of the carb
if you cover it with your hand.
Be careful doing this as it could backfire,
maybe try it with the plug wire grounded.

If you have a good spark on the rear cylinder
try some starting fluid in the carb mouth to see if
it will run on that.
If it does then you know there is
a fuel/vacuum problem.

Also check the carb slide is functioning.

If the carb is full of fuel and
the jets are clear and the
cylinder vacuum is happening
it has to draw fuel in.

So,
-verify the fuel level in the carb with a hose.
-verify the spark,
-check for cylinder compression/vacuum,
-check for intake air leaks.
-check for suction on back of carb.
-try starting fluid to see if cylinder can run or not.

Good luck!
Wayne S.
----