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From: Nichts on 1 Sep 2009 15:52
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.
From: paul c on 1 Sep 2009 17:46
Nichts wrote:
> 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.

There are two or three serious carb' experts here who know much more
than I do and they usually pipe up so I won't try to give detailed
advice. I looked at
http://www.bikebandit.com/houseofmotorcycles/honda-motorcycle-cl350k4-1972/o/m9205

which is for a cl350k4, but I can't quite figure out which screw is the
mixture screw and which side of the needle it's on. If the screw you're
adjusting is on the engine side of the throttle piston/needle, I think
that would be a fuel screw and 4 or 5 turns out is probably way too
rich, maybe the screw is about to fall out of its threads! If I've got
that right, turning it clockwise would make the mix leaner. Maybe
somebody will suggest a starting point, the range for many Hondas seems
to be between 1 1/2 and 3 turns. It's easy to bungle synchronization if
you pick a starting point that's way out of range.
From: Nichts on 1 Sep 2009 18:12
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.
From: 1949 Whizzer on 1 Sep 2009 18:19
On Sep 1, 12:52 pm, Nichts <uhhh...(a)gmail.com> wrote:

> Another very silly question:  which direction do you actually turn the
> mixture screws to lean it out?

Clockwise.

> From what I've gathered, turning them out (counterclockwise) should be
> lean,

Wrong.

> but even when I turn them out like 4 or 5 turns, the plugs still foul.  

Idle mixture screws stop having any effect on the idle mixture
delivered to the idle mixture port after about three turns
counterclockwise.

A site called oldmanhonda.com used to have a list of jet sizes and
starting points for setting the idle mixture screws and air screws of
all the first and second generation Hondas, but I can't find it.

I recommend that you screw your idle mixture screws all the way in
until they just gently bottom out, then turn the idle mixture screws
counterclockwise one full turn and see how that works.

If you turn each idle mixture screw clockwise 1/4 of a turn and give
the engine a chance to burn off any rich mixture and then the idle RPM
increases a little bit, turn the idle SPEED screw a little bit
counterclockwise so the engine slows down to the specified RPM in the
manual.

Then try turning the idle mixture screws clockwise another quarter
turn and let the engine use up any exces mixture and see where the
idle RPM goes.

Some manuals recommend that you use a precision tachometer to
determine when the idle RPM drops off 50 RPM as you reach the critical
adjustment on the idle mixture screw.

When it drops off 50 RPM, you tweak the idle mixture screw
counterclockwise
again to get that "perfect" idle mixture (for the particular weather
on that particular day).
From: frijoli on 1 Sep 2009 21:52
Nichts wrote:
> 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.
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.

Clay
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