Carb problem?

Righty-ho; if a four cylinder engine starts on the button ok but idles
roughly (three or four cylinders, seemingly), has very poor throttle
response (it "lags" behind opening the throttle) and remains rough until
3-4k-ish rpm then seems to clear, plus, when at speed on, say, the
motorway at ~4-5krpm, pops and bangs with ickle flames from the zorst,
what's the most likely cause of this?

My (limited) experience suggests it's likely to be the carbs either set up
wrong (or worse), but might also be a weak spark, dodgy timing, etc.?

It's a 1989 CBR600, btw. and has (supposedly) been Dyno-jetted at some
point, new plugs ~6 months ago. It has been stood for a while, but tank
has been emptied and fresh go-juice inserted.
--
| Wik -UKRMHRC#10- 2003 R1150GSA -DC#1 -'FOT#0 'FOF #39 - BOD#12 BOB#12
|# You don't believe me | "Experience is the worst teacher.
|That the scenery | It always gives the test first
|Could be a cold-blooded killer. | and the instruction afterward."
***** human response from wik at blueyonder dot co dot uk *****

 

Sounds like fuel problem. As it appears it's been standing for a while I
reckon it'd be a good idea to clear out the carbs and ensure no leakage
around any form of rubber joints between them and the engine.
Popping and flames might suggest unburnt fuel going through into the cans
and after a while at higher/hotter revs igniting.


--
--
Robbo
1500GL 1988 Goldwing (Rebuild in process)
BMW K100 RS 1984
"Fairly Quick" status. Silver level
BotaFOF #19. E.O.S.M 2001/2002/2003.
B.O.S.M 2003.FURSWB#1 KotL..YTC449
PM#7

 

Hmm...before tearing the carbs apart (do Honda do "rebuild kits" for
these like I used to get for Yankee V8 carbs?) is there 'owt else I can
(easily) check for?

Glad to see the .sig's got shorter, but yer sep is still borked...
--
| Wik -UKRMHRC#10- 2003 R1150GSA -DC#1 -'FOT#0 'FOF #39 - BOD#12 BOB#12
|# You don't believe me | "Experience is the worst teacher.
|That the scenery | It always gives the test first
|Could be a cold-blooded killer. | and the instruction afterward."
***** human response from wik at blueyonder dot co dot uk *****

 

Probably not. If they have been Dynojetted, they will be difficult
to return to their virgin status.
You will need new needles, needle jets and main jets,
possibly nylon spacer washers that hold the needles,
and either new slides or some method (araldite) of
reducing the oversize bleed holes to standard.
You may want to replace the diaphragms while you're at it.

 

My bet is on the ignition system somewhere. I've had plenty of problems
that I thought were fuel-related, and it's always turned out to be the
ignition. Plug caps, HT leads, coilscoilscoils, etc.

Depends how long it's been stood for, mind. How long is "a while"? Six
months? Unlikely to be fuel related. Two years? probably is.

 

On Thu, 26 Feb 2004 21:02:09 +0000, The Older Gentleman yammered:

[snippo]

[noted]

But would that explain why the problem all but vanishes when the revs
build?

It had a dribble in it when first viewed and on collection from the owner
he'd put a couple of litres in. We brimmed it full of BP's finest at the
earliest opportunity.

Oh and one other oddity which, now you mention electrickery makes me rub
my chin pensively, the rev-counter doesn't work and apparantly, never has.

Could it be he's bolloxed the ignition when swapping the speedo? I know I
was a tad puzzled when fitting the "de-restrictor" to Suze's CBR4 that it
had a feed from the "clocks" to the HT coils...

If matey's put different clocks on it, maybe it's missing summat vital...
--
| Wik -UKRMHRC#10- 2003 R1150GSA -DC#1 -'FOT#0 'FOF #39 - BOD#12 BOB#12
|# You don't believe me | "Experience is the worst teacher.
|That the scenery | It always gives the test first
|Could be a cold-blooded killer. | and the instruction afterward."
***** human response from wik at blueyonder dot co dot uk *****

 

Stood? Right then - it's blocked pilot jet in one (or more) of the
carbs.

 

Yes. I've had similar problems with Alfa 4 pots. Not mentioned it before
cos I don't know how different bike engines are. It was explained that
they run better at high revs on 3 cylinders cos there is more power
available to take up the slack as it were/
--
Catman MIB#14 SKoGA#6 TEAR#4 BOTAFOF#38 Apostle#21
Tyger, Tyger Burning Bright (Remove rust to reply)
Alfa 116 Giulietta 3.0l (Really) Sprint 1.7
Triumph Speed Triple: Black with extra black bits
www.cuore-sportivo.co.uk

 

Nice. Short, concise and to the point. Bit like Suze, really.


I feel a trip to Honda Chiswick coming on...
--
| Wik -UKRMHRC#10- 2003 R1150GSA -DC#1 -'FOT#0 'FOF #39 - BOD#12 BOB#12
|# You don't believe me | "Experience is the worst teacher.
|That the scenery | It always gives the test first
|Could be a cold-blooded killer. | and the instruction afterward."
***** human response from wik at blueyonder dot co dot uk *****

 

What for? Take the carbs off, remove the float bowls, remove jets,
blow through, assembly is the reverse etc.

The Online ZX7 wouldn't start when I got it. It'd been standing, and
the pilto jets (which are *very* small) were all gummed up.

 

<sheepish>

Umm, bits?

Oh aye, it's the "blow through" bit that I can't get -- I once owned an
ickle hobby compressor, but it's long since gone. I'm aware one shouldn't
stick stuff (other than petrol/air) through the jets, although this never
stopped us when drag-racing...

Mmm. Some Wynns will be required, also...
--
| Wik -UKRMHRC#10- 2003 R1150GSA -DC#1 -'FOT#0 'FOF #39 - BOD#12 BOB#12
|# You don't believe me | "Experience is the worst teacher.
|That the scenery | It always gives the test first
|Could be a cold-blooded killer. | and the instruction afterward."
***** human response from wik at blueyonder dot co dot uk *****

 

Heh. "I'm hard to get, Steve. All you have to do is ask me ..."