NGPZ: Idle oddities on range bikes

[Steven Bixby]

I do some (under)paid mechanic work for a local MSF school, and I have
two bikes acting a little strange.  The school runs Kawasaki
Eliminators - 125cc twins, as well as others - (Nighthawk 250's, Suz
DL200's, a couple Honda Rebel 250's, stuff like that).

Anyhow.....   I have two of the Eliminators with some strange idle
issues.  One of them started got pulled out of the rotation because
the idle kept climbing higher and higher after a throttle blip.   The
cables were nice and smooth, the butterfly was free-turning, etc.   I
figured there might be some crap in the slide and/or main jet, so I
pulled the carb off and cleaned it out as best as I could do sitting
in the range parking lot. (They have garden variety Mikuni carbs.)

I put it back together and now, while it doesn't *climb*, the RPM's
are slow to drop to idle.  If I rev it up to say 5-6K rpm, then
release the grip, it'll drop to about 2000 rpm and then to idle (maybe
1200rpm?) over a 3-5 second period.  (RPM's are via mental-tach, since
the bikes themselves don't have tachs.)

For a novice, this probably isn't an ideal thing.  And there's now two
bikes acting like this.  Any theories on what could cause a CV carb to
act this way?  It almost sounds like some kind of orifice is plugged
down, but I don't know enough theory behind CV carbs to guess.