.......

So I've had the bike out today for awhile, and after having swapped
the plugs with fresh ones and carefully tuning the carbs as outlined
above, it seems to be going along significantly better. The plugs got
a little fouled (just a dusting...this is quite monumental, though),
but that's probably because in my eagerness to ride it, I forgot to
let any excess burn off. I will brush them off again tomorrow, and
tinker with it a little more. Thanks a lot guys. You'll probably be
hearing from me again soon. I expect this bike to be fairly high
maintenance.

 

If you're running the correct heat range spark plugs, the porcelin
insulator inside won't be tan like it would be if you well using
leaded gasoline.

There should be a ring of black soot maybe 1/8th of an inch wide deep
inside the plug where the insulator and the steel body of the plug
meet.

Experienced tuners have a magnifying flashlight to inspect the spark
plug to see if the ring exists. If there's no soot deep on the
insulator inside the plug, the mixture is too lean.

Soot on the exposed end surface of the threaded part of the plug is
meaningless, as the cylinder head temperature will only reach 350~375
degrees.

If you see any brown color on the plug that's oil being burned, unless
you are using an octane booster for some strange reason.

 

However, you should realize that the expert tuners are checking the
plugs after a hard run for several miles and a "clean cut" during
which the engine is shut off and the clutch pulled in and the
motorcycle is stopped without the engine ever being allowed to idle
and cover up the mixture indications with extra soot.

The CV carburetor used on motorcycles since about 1970 is a mysterious
device to most tuners who have no idea whatever as to the intention of
the designer.

The whole idea of a CV carburetor is to take direct control of the
midrange and high speed circuits away from the rider. This makes the
engine run leaner and cleaner most of the time the rider is cruising
along at small throttle settings.

And the idle mixture screw works opposite from the air screw that
older slide valve carbs had.

Turning the air screw clockwise richened the mixture, turning the idle
screw clockwise leans the mixture.

And tuners who are trying to "lean out" the idle mixture wind up
turning the idle mixture screw counterclockwise too far, so they have
to turn the idle speed up to compensate for excessively rich idle
mixture.

Most amateur tuners don't realize that there is a pattern of three
acceleration transition ports that are controlled by the lower edge
of
the throttle butterflies.

If a CV carburetor is unresponsive to the idle screws, the first
thing
to do is turn the idle speed screws counterclockwise to close off the
acceleration transition ports.

If you have a set of CV carbs on the bench and look into the
downstream side, what you should see is just half of *one* of the
three transition ports, the other two will be covered up by the
closed
butterfly.

The transition ports are not affected by the adjustment of the idle
mixture screw at all. They are controlled entirely by the position of
the butterfly.

You cannot set the idle mixture if the throttle butterflies are too
far open because the engine sucks unregulated mixture from the
transition ports.

However, if the excessive richness is *not* due to the butterflies
being too far open, the other possible culprits are stuck float
valves
or floats that are adjusted too high, causing too much fuel to
accumulate in the float bowls.

When the fuel level is too high, the engine can easily suck too much
fuel through the idle jet because it takes less engine vacuum to suck
the fuel up.