Motorcycle Repair: Motorcycle problem, kawasaki zx600, air fuel ratio

Question
Hello Wayne,
I own a 1999 Kawasaki zx600.  The problem is that when am in 6 th gear and cruising, if I engage the clutch and let off the throttle, the bike wont idle and it shuts off. I then have to stop and get it going again. I found out that if I engage the clutch and ramm up the engine a little before the rpm's go all the way down, the bike wont shut off.  This is very fustrating because it only does it on 5th and 6th gear.  It wont do it on the lower gears.

Answer
Jose,

at high speeds the engine and clutch are
turning fast, when you pull the clutch
and close the throttle there is still
alot of clutch drag until the rpms drop.

The clutch drag may be excessive due
to adjustment, worn plates or sticky oil.
Try some different oil or clean the clutch
plates, check for warpage.

The other thing is during fast decelleration
the pilot (idle) system cannot deliver enough
fuel to create a normal, combustible air/fuel ratio.
The mixture becomes too lean to burn reliably
in the combustion chamber causing the engine to stall.

You can try using a faster idle or perhaps
trying one size larger idle jets.

Make sure the carbs are clean and the
gas tank fuel valve is in good shape.
Check for unwanted pressure in the tank
this is caused by plugged tank vents.

The fuel valves are opened by engine vacuum,
there is less vacuum at high speed and
more when the speed drops.
This change in vacuum may cause problems in fuel
delivery if the fuel valve has bad rubber diapragms.

Replace the fuel filter.
Fuel is very bad these days for plugging carbs
quickly. If the bike is not used frequently
use a fuel stabilizer.

Check your spark plug colors, black is too much fuel
tan color is about right. White is lean and bad
for engines. You can learn alot about how
the bike is running from the plug color.