Idling too fast

I'm sure I've heard of this problem before, but I can't remember what
the cause or solution is...

I've started balancing the carbs on the GSX600F. According to the HBoL,
I set the idle speed to ~1750rpm, and start by balancing 3+4, then 1+2,
then (1+2)+(3+4), IYSWIM.

Easy enough, I thought, but: 3+4 were *way* out, and the nearer they are
to being balanced, the higher the idle speed; like, *really* high,

So, what's causing that then? I've got a feeling it's an inlet rubber
problem, but I'm not sure why... any suggestions?

 

Is there a big difference between 2+3?

A mate of mine borrowed my carbtune and got it a bit arse about face. He
wound the centre screw until (3+4) were nearly dragging the mercury to the
stops and the bike was screaming away at 4,000+rpm. He did get (1+2) in
perfect balance though

As the revs increased, the balance twixt 3+4 appeared to even out, so he
dropped the idle on the adjuster until it was fully backed out and carried
on oblivious. It was only when the engine was screaming he rang me....

Try adjusting the centre screw to get 2+3 in balance, then the left screw to
get 1+2, the right screw for 3+4 then a little tweak on the centre screw
again. I always found that easier on my teapot than 3+4, then 1+2 then 2+3.
Same on my Bandit, I just find it easier to get to 1/2 a graduation mark on
the scale doing it that way, YMMV

 

Idle speed always increases as you balance the carbs. It doesn't matter,
as long as they're all reading the same. Get them all reading the same
on the gauges, and then turn down the idle speed.

 

Not now there isn't, no. But that's a bit academic unless I can get the
idle down to something sensible.

Hmmm... I'd give it a go, but they're all pretty close now. I'm not that
fussed about playing about with them again, unless it's going to help
the idle problem.

 

Moon Badger says...

You really should treat 3 as the datum, try and keep that reading
constant and not change its height on the gauge. Wind the right screw to
get 4 to meet it and then adjust 1 and 2 to match each other. After you
have that sorted you balance the two pairs to match each other by
adjusting the centre screw.

It's not that difficult if you don't have air leaks. When I start I
always wind the tickover up so the bike is at 1,500 revs to start with,
the engine runs a lot smoother there and makes balancing easier.
Obviously you wind the tickover back down once balancing is completed.

 

3 is the datum. The left screw does 1 ( or 2, can't find the Haynes ), the
centre screw does (1+2) against 3 and the right screw effectively only
controls 4.

Champ pointed out throttle cable slack and clamps, worth checking. FWIW,
I've used vaseline ( feed lines 'R' us ) smeared on carb inlet rubbers to
check for leaks. It fill the cracks ( oo-er ) temporarily and doesn't
damage the rubber.

Another thing worth checking for is crud on the mechanism, especially
embedded crud in the springs stopping the butterflys from closing fully.

 

Moon Badger says...

Spray carb cleaner onto them, if the revs rise you've got a leak.

 

Oh yeah. Duh.

 

I'm glad somebody's paying attention.

I unhooked it, just to make sure.

They are, but I'll double-check.

 

.... is what I'll be trying next.

 

Rope - as useful as ever.

 

Well, that didn't help.

I did notice something potentially interesting though, while I was
fiddling about: uncovering the vacuum connections whilst the engine's
running causing the engine to die (well, duh)... but not, apparently,
#4, which appears to make no significant difference to the running of
the engine.

Methinks that #4 is not a happy pot...

 

Not really, Spike.

 

"Leaking air internally"? What, into itself? ;-)

Hmmm... how much do compression testers cost? Do you think Santa would
bring me one for Christmas?

 

A mate of mine had terrible trouble getting a Morini to idle properly
after he had to have a second hand head quickly put on just before a TT
trip. Even with only two cylinders, a mercury manometer gauge and an
expert on hand (not me) we couldn't get it right. The expert eventually
reckoned the used head must have had a slightly burnt valve.


--

+-------------------------------------------------------------+
| Pete Fisher at Home: |
| Voxan Roadster Gilera Nordwest Yamaha WR250Z |
| Gilera GFR Moto Morini 2C/375 |
+-------------------------------------------------------------+

 

Gunson compression guage is £18.99 at Halfrauds.....

HTH

Dave

 

Gunson? Is there stuff any good? I'd rather make Santa pay for a decent
one...

 

No idea. Just thought that if you wanted it for a quick one-off check it
ain't much to fork out.....

Dave

 

True... but I like *nice* garage equipment, not stuff that'll fall apart
after two uses.

 

I've got a few Gunson bits - remote starter, compression tester,
multimeter & strobe. They came as a box set around 20 years ago & still
work fine.

--
Krusty
www.MuddyStuff.co.uk
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