Motorcycle Repair: Carbs are to rich, worn piston rings, pilot jet

Question
Yes, i have a 1982 kawasaki csr 305 and i have been trying to lean the carbs out, but no matter what i do it seems the carbs still stay rich. How do you lean them out.

Answer
Hi Robert,

You did not mention what you have tried
or why you think it is running rich
so I will give you what information I can.

First thing you want to do is a spark plug
reading to determine if it is running rich
or lean.

If the plugs are very black and sooty
then it is very rich.
This might be caused by choke being partly on
or plugged air intake or plugged air filter.

Another cause for abnormally rich fuel mixtures
can be a leaking fuel petcock vacuum diaphragm.
This is only if you have a vacuum operated
fuel valve.

If your spark plugs are wet it could be fuel
or oil.
The float level could be too high in the carburetors.
Oil is due to worn piston rings and cylinders.

If the float levels are correct and the float
needles/valves are not leaking then
rejetting is done by reading the spark plug color
and downsizing the center brass main jet
in the carbs.

The main jet is directly in the carbs center and has
a small jet screwed into it's center.
This is the jet that controls most
of the fuel taken in from 3/4 to full throttle.
It can have some effect at other speeds as well.

If you want to lean out the idle mixture
then you would reduce the idle pilot jet
which is off to the side of the main jet
and is recessed. It may even be covered with
a small rubber plug. If these plugs are missing
you may have some erratic running due to that.

Use caution when downsizing jets as
this can cause overheating and burning
of the pistons.

Always do a fast quick run after rejetting with clean spark plugs
and read the plug color.
It is ideally a light to medium tan color, too light is too lean
and too dark is too rich.

Check your air filter and intake first and
then make sure the carbs are very clean.
Even plugged pipes or mufflers can cause a
rich running symptom so try to eliminate
common causes first.

Usually going down a size or two on main jets
will have some effects.
The needle in the carb slide can sometimes
be lowered to lean the mid range fuel mix.
If you raise it then the mixture gets richer.

Idle fuel screws have little effect on the mixture
overall. Turning it inward or clockwise a bit might
lean the idle fuel slightly.

Luck!
Wayne S
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