'87 CBR600: Lo-speed miss

 
'87 CBR600, 20k easy mi.

I've never been a torque-bigot, never owned a big Harley twin, but when
I bought my first (and only) crotchy-rocket back in '88, the 1st  thing
I tested for was lo-end torque. The bike pulled reasonably well and
smoothly from around 1200 rpm. That and the song it sang from 8k-12k
rpm made me a happy camper.

It continued like that for many years.

For the last 5 years or so, it's had a lo-speed miss. Chokes and burbles
from about 1200-1500 rpm or so. Like its firing on 2 or 3 cyls. Very
annoying in traffic.

I pulled the Keihin CV carbs and cleaned them meticulously May '06.

The easy answer is crud in lower end of carbs. Doesn't seem to fit the facts.

There is a section in my Garbage-Clymer manual on "Pilot Screw Adjustment".
I haven't tried any of it.

There's no evidence that the motor is running either lean or rich.

Any ideas?

  Thanx,
  Puddin'

" ... and the bees made honey in the lion's head."
       - from "If I Had My Way", Blind Willie Johnson

 


Plugs and/or wires.

Wild idea: Battery (or charging system) about ready to shoot craps and not
providing enough voltage to the ignition system at low rpm's.

Somehow I didn't get from your message whether your carb work made the
situation better or worse or no change ??

 

But it runs great from about 1800 rpm to 10+k. Anything above around
1800 rpm feels fine.


No change.

  P

" ... and the bees made honey in the lion's head."
       - from "If I Had My Way", Blind Willie Johnson

 

Your idle ports and passages are probably plugged up with gum and
varnish from evaporating gasoline. If you can squirt some Berryman B12
through the pilot air jet (it's probably in the air inlet bell of the
carburetor) and the B12 comes out through the three transition ports
downstream of the butterflies and the single idle mixture outlet port
that is about another inch downstream of the transition ports, your
idle passages are clean enough to adjust the idle mixture screw open
another 1/4 of a turn.

Setting the idle mixture screws too rich may slow the engine idle
down, and then, when you turn the master idle speed knob up, the
transition ports will be uncovered prematurely and the engine will
idle too fast after you blip the throttle.

 

I think it's back by the manifold boot ...


There's a fair amount of detail in what you say. Is it really
specific to Keihin CV's on an '87 CBR600? Or is it kinda generic
and hopefully applicable ... ?

  Thx,
  P

" ... and the bees made honey in the lion's head."
       - from "If I Had My Way", Blind Willie Johnson