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From: paul c on 2 Sep 2009 00:19
Nichts wrote:
> Hey, thanks. Yes, in that blow up, the mixture screw is labeled part
> number '8'. I should have mentioned above that even when the mixture
> screws are turned in nearly all the way (when fully seated the engine
> just putters down and dies) and I ride it for a bit, I still get
> carbon fouling! It's quite boggling, really. Also, my choke is not
> on. That's the first thing to check, of course.
>
> A factory spec-sheet that I found said 3/4 of a turn, which I've
> tried. I've also tried, a full turn, 1 1/2 turns, etc. It shouldn't
> have to be quite so accurate, anyhow. I don't even have different
> grades of carbon fouling, no matter how I adjust the carbs, if I ride
> it for about two miles and pull the plugs, they are coated in carbon.

I see some of the big guns haven't answered yet, so I'm curious whether
the "fouling" is the only apparent "problem"? Does it start easily in a
second or two when cold? Does it respond well at different amounts of
throttle? Does it smoke? When starting from cold, when you put your
hand on the headers for the first minute or so, do the cylinders seem to
warm up equally? Are the plugs new and was the bike not ridden very
fast in recent history (if the bike has a history of mostly being ridden
slowly, it may take a long time for the plugs to burn off some of that
carbon). Sounds like the idle jets are clear, could the float levels
be way out of whack or the piston needle be set very high up? Not
asking for answers, maybe one of those questions might trigger an idea.
From: 1949 Whizzer on 2 Sep 2009 01:28
On Sep 1, 6:52 pm, frijoli <c...(a)dud.gov> wrote:

> Turning in goes lean. Carbon on your plugs really has little
> to do with your Idle mixture screws, unless you ride around
> 99% at idle.

When you ride a motorcycle with CV carburetors, you *are* riding
around on the idle mixture most of the time. That's why it's so
important to get those idle mixture screws set right.


From: 1949 Whizzer on 2 Sep 2009 19:48
On Sep 1, 3:12 pm, Nichts <uhhh...(a)gmail.com> wrote:

> I should have mentioned above that even when the mixture
> screws are turned in nearly all the way (when fully seated the engine
> just putters down and dies) and I ride it for a bit, I still get
> carbon fouling!  It's quite boggling, really.  Also, my choke is not
> on.  That's the first thing to check, of course.

I didn't see that message yesterday while I was posting my reply to an
earlier message.

If the carburetor is unresponsive to the idle screws, the first thing
to do is turn the idle speed screws counterclockwise to close off the
acceleration transition ports.

Most amateur tuners don't realize that there is a pattern of three
acceleration transition ports that are controlled by the lower edge of
the throttle butterflies.

If you have a set of CV carbs on the bench and look into the
downstream side, what you should see is just half of *one* of the
three transition ports, the other two will be covered up by the closed
butterfly.

The transition ports are not affected by the adjustment of the idle
mixture screw at all. They are controlled entirely by the position of
the butterfly.

You cannot set the idle mixture if the throttle butterflies are too
far open because the engine sucks unregulated mixture from the
transition ports.

However, if the excessive richness is *not* due to the butterflies
being too far open, the other possible culprits are stuck float valves
or floats that are adjusted too high, causing too much fuel to
accumulate in the float bowls.

When the fuel level is too high, the engine can easily suck too much
fuel through the idle jet because it takes less engine vacuum to suck
the fuel up.


From: Dave on 9 Sep 2009 14:06

"Nichts" <uhhhmmm(a)gmail.com> wrote in message
news:787ae48d-fabb-4a95-bc21-909a890372cd(a)q35g2000vbi.googlegroups.com...
> Hey folks, I've a 1972 Honda CL350 with some apparent carburetor
> issues. The jets are the factory ones, so this doesn't have to do
> with jet size. I have gone through the standard procedure of tuning
> them ( Warm the engine, adjust the idle to ~1100rpm, turn the mixture
> screws on each until engine idles at it's maximum, equalize exhaust
> pressures via the idle speed screw again, until the engine falls back
> to 1100 rpm...) Even after running through this my plugs end up carbon
> fouled after riding for a little while, and no matter which way I turn
> the idle mixture screw, it still happens. I noticed that the primary
> main jets in each carburetor do not have an O-ring on them, and it
> looks as if they should by the groove(s) around their circumference.
> Possibly, the lacking O-ring is allowing too much fuel to be sucked up
> around the jet holder and into the bore??
>
> Another very silly question: which direction do you actually turn the
> mixture screws to lean it out? From what I've gathered, turning them
> out (counterclockwise) should be lean, but even when I turn them out
> like 4 or 5 turns, the plugs still foul. Any advice for an amateur
> like myself will be greatly appreciated.

Does the bike start easily when cold? Idle well when warmed up? How's the
acceleration? From idle to 2K? From 2K-5k? From 5k-redline? Does it
stutter or hesitate at any throttle position? You'll have to set up the
correct main jet first. If the jets in it are originals and there are a
zillion miles on the bike (or if some previous owner changed the size) they
may be oversize from factory stock. Is the needle height adjustable?

From: 1949 Whizzer on 9 Sep 2009 15:28
On Sep 9, 11:06 am, "Dave" <dspear9...(a)yahoo.com> wrote:

> Is the needle height adjustable?

Needle height really isn't all that important, but amateur tuners will
often stack a few 0.5mm washers under the head of a non-adjustable
needle.

They think they are really smart when they do this, but what they are
doing is just causing the needle to allow gasoline past the needle jet
slightly sooner, they aren't affecting the peak power of the engine,
they are affecting the midrange, and it's possible that the engine
isn't producing enough vacuum at lower RPM to lift the slide enough to
take advantage of extra needle height anyway.

www.factorypro.com has some *really* good tips about CV carburetor
tuning and troubleshooting that the manufacturers of competing jet
kits don't want you to know.

For instance, there are pictures of needles that are badly worn and
needle jets that
are *subtly* worn in an egg shape so that gasoline can get past them
at small throttle settings, like less than 1/4 of the slide lift

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