Re: '87 CBR600: Lo-speed missOn May 23, 7:21 pm, Puddin' Man <puddingDOT...@gmail,com > wrote:
> On Thu, 22 May 2008 21:31:46 -0700, red bowfire <red bowf...@SPAMsbcglobal,net > wrote:
> >Puddin' Man wrote:
> >> '87 CBR600, 20k easy mi.
>
> >> <snip>
>
> >> 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.
>
> > If nothing was done mechanically to cause this then I'd have to say
> >it's possible something inside the carb has worn out to create a rich
> >condition. Got any spark plugs showing a lot of carbon?
>
> Nope. Pulled #1 and 2 plugs not long ago. Looked normal.
>
>
>
> >> The easy answer is crud in lower end of carbs. Doesn't seem to fit the facts.
>
> >I had the same thing happen when my Charcoal Cannister screen broke and
> >filled the float bowls with charcoal. If your float bowls are completely
> >clean then I'd go with the above.
>
> The bowls were *extremely* clean when I pulled carbs last season. Bike
> has had very little use since.
>
>
>
>
>
> >> There is a section in my Garbage-Clymer manual on "Pilot Screw Adjustment".
> >> I haven't tried any of it.
>
> >If you're looking for the adjusters, look on the right/exhaust side of
> >the carbs in the lower front corner of the carb. If the non tamper caps
> >are still on you will see a small grey screw head that will have limited
> >movement (1/4 turn max each direction). I pried the caps off to find a
> >smaller brass screw head underneath which was not limited in movement.
>
> >> There's no evidence that the motor is running either lean or rich.
>
> > Check out Factorypro,com / Product Tech Support / CV Carb Tuning
> >section for some tips on troubleshooting lean/rich conditions.
> > I took my carbs apart for cleaning and played around with the throttle
> >needle height, pilot screw setting, and main jet quite a bit. Why? I
> >bought the bike with stock jetting and a Yoshimura full race only
> >exhaust already installed. Ran super lean I had a few flat spots I had
> >to dial out. I can go into more details on what I found/fixed, if you
> >need the info.
>
> My bike is 100% stock and I got no evidence (via plugs) of a mixture
> problem.
>
> > One indicator I used when I was tuning: If I revved the bike, and it
> >'hung' before dropping down to idle, then it was too lean. If it dropped
> >down to idle like a brick, it was too rich. Then I'd adjust the pilot
> >screw and needle accordingly.
>
> I've not noticed either condition.
>
> > I've got two ideas. 1) Something has worn inside the carb allowing too
> >much fuel to bog down the bike at those rpms. A float valve/leaking
> >jet/or even worn throttle needle 2) A few years ago my
> >Regulator/Rectifier melted and failed. I replaced it with a salvage yard
> >(yet good) R/R and a fresh battery. The bike never fired up/idled and
> >accelerated so smooth. After a few months, the stumble I had came back
> >to normal, and just last year my second R/R burned up.
>
> Hmmmmm. Interesting.
>
> > As a side note, in the 15 years I've had it, I've had 6 batteries die.
> >I have an electrical issue I haven't really troubleshot yet (stator).
> >It's been a great bike otherwise.
>
> Problem symptoms?
>
> Back in the 90's it took po' me 2+ years to diagnose/fix an intermittent
> elec. problem (failed to start at unpredictable times). It was the
> pulse generator.
>
> Thx,
> P
>
> " ... and the bees made honey in the lion's head."
> - from "If I Had My Way", Blind Willie Johnson
The famous endings of Monty Python were: "And now for something
completely different"
It seems you have correct and clean carbs.
Maybe an IC igniter that has trouble timing low revs? I'd check
timing with a stroboscope.
Rob.