relentless carbon fouling problem

Socrates was the greatest troll ...

 

When I cleaned the carbs I didn't know what to look for. Definitely the
float valves and the bowl-to-body O-rings were at best marginal. Maybe
I only dreamed that the jet needles were flat on the sides. The big
cost of the overhaul is the R&R of the carbs. It doesn't take an extra
five minutes to replace the jet needles. I'll compare the new and old
parts to make sure they are the correct replacements.

Anyway the downtime is killing me. And by swapping other parts (eg
floats) between carbs and noting whether the fouling moves to the other
side, I can probably settle the question of whether there was a
carburetor problem.

 

The downtime is a major part of the hobby of fixing old crocks. You
happily work on them during the winter when it's too cold and rainy to
ride. You sing Steppenwolf to yourself as you work, "Get your motor
runnin', Get out on the highway..."

But, if you don't finish the project before the good weather comes, you
stash the bike away for the off season again and go ride your *other*
machine to go "Lookin' for Adventure, And Whatever comes your way."

If riding is in your blood, you'll have *another* motorbike that runs,
so you don't have to ride one that needs work. I have four bikes, so I
always have something running...

Is that old Honda taking you away from family and friends? Don't let a
broke motorbike do that...

 

"I don't want a pickle ..."

http://www.arlo.net/lyrics/motorcycle-alice.shtml

 

I just came from the auto parts store where I talked to two guys who own
motorcycles and seemed to know something about them. One of them said
that the job of the idle mixture screw was to let air into the mix.
They said that turning the screw in would make the mixture richer and
turning it out would make it leaner.

My owner's manual says "Turning the pilot screw in produces a lean fuel
air mixture, turning the screw out produces a rich mixture."

I supposed the screw to be simply a valve that throttles the flow of
fuel into the mix, and that you close it by turning it clockwise.

Maybe those guys were thinking of some other type of carb.

 

That's true of a slide valve carburetor, such as the Mikuni VM series
that was used on dirt bikes and older street machines. The slide valve
carbs didn't have diaphragms or throttle butterflies, they just had a
cylindrical slide that was raised and lowered directly by the throttle
cable...

The idle mixture screw could by found on the side of a slide valve
carb, in the passage that admitted air to the idle circuit. So, what
they said was at least half true. But it doesn't apply to your CV
carburetor-equipped machine...

Yes, if you have constant vacuum carbs, and the idle mixture screw is
downstream of the throttle butterflies, turning that screw clockwise
does lean out the mixture

It's a tapered needle that closes off an orifice that fuel/air mixture
is passing through. The fuel and air are already mixed before they get
to the idle screw...

That's correct. They were thinking of slide valve carbs...

 

I was looking on the wrong page. The valve stem seals are P/N
12210-362-005.

 

Moot point: Any gasket kit should include a set (unless you
insist on genuine Honda parts). Good luck with the carb
rebuild anyhow.

 

I ordered the carb kits last week and got them today. There seems to be
a problem with the size of the main jet. partsfiche.com lists a #110
main jet for the CJ360T, but it seems that I received #100 main jets.

kk, I have presented some details below which could probably be skipped,
but I wonder whether you could remark about using a #100 main jet
instead of the specified #110?



Excruciating details:

On their website, in their ebay auctions, and by email, Sirius
Consolidated presented the KH-0142 as fitting CJ360T and CB360.

partsfiche.com shows these part numbers for CJ360T:
16100-388-014 CARBURETOR ASSY. 529.99
99114-246-1100 JET, MAIN (#110) 4.99

They show these for CB360T:
16100-369-004 CARBURETOR ASSY. 313.99
99114-246-1000 JET, MAIN (#100) 5.99

Since I ordered, siriusconinc.com has changed the photo of the KH-0142
kit. The Keyster kit as pictured today lists the following parts. The
kits I received did not come with a parts list, but they would seem to
be the same as those pictured today and listed here:

GASKET, CHAMBER
NEEDLE VALVE
JET, NEEDLE
SCREW, AIR
SPRING, AIR
JET, MAIN #100
JET, SLOW #35
'O' RING
WASHER

Both kits refer to "Original Carburetor No. 16100-369-000".

kk, it seems you mistook the air screw for Jet #68.

When I tore down the carbs previously, I don't remember seeing a part
like the metal washer in the upper right of the photo.

 

Well, the #100 main jet would have an orifice hole that has a diameter
of
1.0 mm, so the area would be 0.7854 square mm, but the #110 main jet
would have an area of 0.9503 square mm...

0.7854 divided by 0.9503 = 0.8264, so the area of the #100 main jet is
about 17.4% smaller than the #110 main jet. Theoretically the #100 main
jet should flow 17.4% less gasoline when the throttle is wide open, if
the engine develops enough vacuum to pull the maximum amount of fuel
from either size jet...

And there would be #102, #105 and #107 main jet sizes between the
theroretically correct #110 size and the #100 size that came in the
kit, so the #100 main jet is 4 sizes smaller than you think you need
from reading the parts fiche...

If the #110 jet is correct for sea level conditions, the #100 jet would
be
Ok for Denver on a warm day, as air density at 5000 feet above sea
level is
about 14% less than sea level on a 59 degree day...

You could send the kits back and complain, or you could buy brand new
jets for $4 or $5 apiece and spend $10 on shipping and handling, or you
could use the #110 jets that are theoretically in your carbs now. Only
you know how far you want to chase perfection...

Are they actually #110's, do you remember?

Sometimes the repair plans we make don't turn out quite as perfectly as
we planned and we wind up having to re-use old parts and wonder if
we've accomplished anything for all of our planning and ordering and
waiting...

 

I just checked and found that the carb has #110s. Also I don't see any
reason to replace them. Not clear how they can wear out, and the
orifice looks too big to get plugged. Well at least I have the #100s in
case I ever feel like trying to outguess the engineers ... unlikely ...

Both slow jets were partly plugged, seemingly from rust that I was
surprised to find in the bowls.

The needle jets in the kit are noticably more slender near the tip than
the originals. I didn't detect any out of round condition in the
original jet needles or needle jets, so I am still using the originals
for now.

The only parts that really needed replacement were the slow jets. Some
of the original 'O' rings were marginal. Besides the slow jets, the
carbs are somewhat better after the overhaul---ready to last another 30
years, I suppose ...

The best part of the overhaul was that I found a tear in the diaphragm
of the left carb. I moved the diaphragm to the right carb, and now the
right pipe is running cooler than the left.

 

I suppose that main jets could erode over eons of use from gasoline
flowing through them. And, sometimes amateur mechanics will have
buggered out the orifice hole with some harsh steel instrument trying
to clean out the goop that had hardened in there...

Then there are the amateur "tuners" who have a set of fractional inch
sized drills and they decide to drill the orifice out to 1/16th of an
inch, or 3/32's. The professional mechanic needs those jets for the
above situations....

But, any carburetor rebuild kit is usually "overkill", it constains far
more parts than the mechanic really needs, in order to contain that one
part that he does need. Unfortunately, the kit didn't contain the
diaphragm that your are casting about for...

Rust never sleeps. If you haven't cleaned, etched and Kreemed your gas
tank, you probably will, eventually...

That sounds reasonable. When troubleshooting, change only one thing at
a time
to avoid complicating the decision process of which idea to try next...

And you are progressing in your knowledge and wisdom about carburetors.
You can be the Carburetor Zen Master of rec.motorcycles.tech when I
pass through the Mikuni Portal to Ultimate Carburetor Enlightenment...

 

So far my valves haven't burned out, although the paint on the top of my
gas tank is starting to fade away ...

I was surprised because when I drained the 13-year-old gas, I didn't see
much if any dirt or rust in the gas or in the tank, and there was only a
little rust around the (original) filter screen. Anyway yesterday
before I tried the newly-cleaned carbs, I ran a swab through my fuel
lines and installed an additional inline fuel filter. I'll evaluate the
filter by draining the bowls after a while.

 

I could easily be wrong, but I guess that Poiseuille's Law applies
(viscous incompressible fluid flowing through a uniform tube).

If so, the flow rate goes like the square of the area (like the fourth
power of the radius) of the pipe. So if the areas were in the ratio
0.8264 to 1, the flow rates would be in the ratio 0.8264 squared to 1,
namely 0.6829 to 1.

http://www.google.com/search?num=100&hl=en&lr=&safe=active&biw=1070&q=poiseuille&btnG=Search

 

http://hyperphysics.phy-astr.gsu.edu/hbase/ppois.html

 

Can you point me to anything online that lists such information about
jets?

I see some jets at denniskirk.com, but I don't know which main jets to
order. I may be a dumbass: My carbs are Keihin. Do I just order the
main jets for Keihin carbs? They also list main jets for RS and HS
carbs. Are those brand names of carbs or some classification of carbs
like CV? The Dennis Kirk online catalog is a train wreck IMO.

http://www.denniskirk.com/jsp/searc...productId=172401725&catId=413&leafCatId=41303

I emailed and they immediately and apologetically
said they would send me the 110's gratis.

I am still very far from perfection. New plugs are fouled after a few
miles. Maybe the 100's _are_ better than the stock 110 jets and it
isn't really a mistake to use the kits as received. I'm going to try to
blame the jets now. I don't know how main jets wear out and I don't
know why I would have to change jet sizes as the bike ages. The
compression is still pretty good---about 150 each side and no smoke
whatsoever.

 

Look for the Sudco International website. I haven't looked at it for
years, since I have a Sudco catalog. There are pictures of various idle
jets in the catalog. None of them is 14MM long as you previously
mentioned.

Also, the Factory Pro website has some nice photographs and at least
they try to sort through all the different jets that you might run
into...

The N102221 Mikuni small round jets with a screwdriver slot are 6MM in
diameter. The N100604 large round jets with a screwdriver slot are 8MM
in diameter. They both screw into the same hole, so they have the same
thread.
You can use Mikuni round jets in *some* Keihin carbs and vice versa.

I think I have a Mikuni main jet in my Kawasaki KLR600 right now....]

Your relentless carbon fouling problem may not be caused by the main
jets, especially if you're not running at wide open throttle a lot. You
would hear the engine blubbering as it fired every other compression
stroke.

That's called 8-stroking. If you open the throttle all the way in a
slide valve carb and the engine starts blubbering, you can just roll
off the throttle and if the engine runs better, you know the problem is
an excessively large main jet, since your hand controls the slide
directly.

A CV carb has its own mind. You may have the throttle wide open, but
what position are the slides in? Is the needle taper still controlling
the mixture by restricting fuel flow, or is the engine running on the
main jet?

You'd need to do some high speed full throttle runs and do plug chops
as I've previously described to sort out your main jets. It doesn't
seem likely to me that going up from a 100 to a 110 is going to cure
your carbon fouling problem.

RS carburetors are radial flat slide carbs for drag racing and road
racing. They are for Japanese inline 4's. HS carburetors are flat slide
carbs for Harley Davidson. Flat slide carburetors have more turbulence
downstream of the slide, so they mix gasoline and air better. The RS
and HS carbs also have accelerator pumps to play with.

Amateur tuners love gizmos and adjustments they can play with...

Accelerator pumps will help the off-idle transition, but if a shade
tree tuner is thinking they will solve the
mid-range flat spot due to the out of phase pressure wave returning
from the
exhaust pipe around 5K to 7K, he's only fooling himself...

 

Thanks.

Since I had the diaphragms replaced, I'm worried that the new diaphragm
material is a little stiffer and heavier than the old and that it may be
keeping the slides from rising as they should, causing a smaller venturi
and a richer mixture.

 

To clarify: I have the old 110's in the carbs now, and I have fouled
plugs. I have new 110's coming in the mail. I have new 100's in hand.
If the 100's are smaller jets, I guess that would give a leaner
mixture. So do you think going from 110's to 100's will help?

 

If the carbon fouling is occurring when you run at full throttle, going
down 4 jets size from 110 to 100 might help. If you're NEVER running at
full throttle, main jets are probably not the problem, it would be
pilot fuel screw adjustment or needle position or float level setting.