cvk34 vulcan 500 carb problem

Okay, I've had these carbs apart a million times. I've synced them,
I've cleaned them, I've done everything I can think of. Bike worked
fine before I hauled it off for a rejet. Bike is a 1997 Vulcan 500 with
CVK34 carbs.

But now I can't even get the bike to run with all original equipment.
I'm at wits end. The bike starts and idles, but when I give it any
throttle it dies out, like its either being starved or being given too
much gas.

Please help!

 

Lean idle mixture could be due to low fuel level in the float bowls,
stuck float valves, plugged up idle passages and jets, or the idle
mixture screws might be set too far closed.

Have you drilled out the EPA anti-tamper plugs yet?

 

Yes, the pilot screws were about 2 turns out when I disassembled the
carbs. They're about 1.5-2 turns now, give or take a quarter turn.

 

What size idle jets are in the carbs now? That's the key to
understanding why your information about the number of turns out is
meaningless.

Since the orifice hole is based upon percentage of a millimeter ( # 30
idle jets having a hole diameter that is 0.3 mm in diameter ), and the
area of the idle jet varies exponentially as to the square of the
radius of the hole time pi, NOBODY can tell you how many turns out the
idle mixture screws should be, you have to find that by
experimentation.

Like, if you work the area formula for a # 45 idle jet vs. a # 30 idle
jet, you'll probably find that the # 45 idle jet passes twice the fuel
that the # 30 jet passes.

Are the floats installed right side up? And when you set the floats
with the carbs on the bench upside down, did you measure from the
bottom of the float (which is the top of the float when it's upside
down) to the metal gasket surface on the carburetor body itself?

When you read the specifications on setting the float level, you might
see a number like
14 mm, plus or minus 1 mm. In this case, since you set the floats with
the carbs upside down, a 13 mm setting is a HIGH float level, making it
easier for the carb to suck fuel out of the float bowls, and 15 mm is a
LOW float level, shutting the fuel flow off earlier and making it
harder for the carb to suck gas out of the bowl.

Do the float valves move freely when you turn the carbs over?

 

Is that the type with diaphragms? (think so) check diaphragms and the
fitting of the slide to diaphragm. If this is loose the slide will not rise
with the diaphragm

 

Bzzzzt! Wrong answer but thanks for playing "I Don't Understand How CV
Carbs Work".

The air is pumped out of the diaphragm chamber through a small hole (or
two small holes) drilled in the slide itself, so loose fitting of the
slide won't affect acceleration from idle.

The slide doesn't need to rise at all for the carburetor to respond to
small throttle openings. The throttle butterfly covers up two of a
triangular pattern of transition ports and partly covers the third
transition port.

When the throttle butterfly moves off the idle setting, it uncovers the
transition ports, allowing sufficient fuel to accelerate the engine
from idle speed.

Only then can the engine pump the air out of the chamber above the
diaphragm, allowing air pressure from underneath the diaphragm to lift
the slide.

If the diaphragm has a large tear, the pressures above and below the
diaphragm will be equalized and the slide won't lift. That's as close
as I can get to your theory about a loose fitting slide causing the
problem.

 

schreef:

The obvious is checking the carbs, but
try to recall what else you did besides working on the carbs.
You could have made an error somewhere else.

Talking about the carbs: what about the connection carb-cylinder.
Leaky?
Rob.

 

B-12 schreef:

Erm.. I read that GaZ ment a loose diaphragm, no longer connected
to the slide, he did not mean too much play beween slide and housing.

Rob.

 

I read on another NG that somene had taken their CV carbs apart and had
not installed the needles correctly. As a reuslt, the needle was not
being lifted as the throttle was turned. If you don't have a shop
manual, go to www.buykawasaki.com and follow the links (many) to the
owner info/parts diagram/motorcycle, year, cc's, etc. for your
year/mkae model. The exploded carburetor parts diagram will show
pretty accurately how the needle and parts fit into the diagram. Good
luck.

Manjo

 

Bzzzt! Wrong answer, but thanks for playing, "I Don't Have A Clue About
CV Carbs".

The symptom is that the engine starts and idles, but dies when given
any throttle.

This indicates that the transition ports are blocked by crud.

It doesn't matter whether the slides rise by being pulled up by the
diaphragms. The needles are straight for almost an inch, no taper at
all, so the orifice area between the needle jet and the jet needle
doesn't change, no extra fuel is admitted to the mixing chamber.

I rode a single-cylinder motorcycle for 20 miles once, with the slide
stuck closed by gum and varnish.

Nevertheless, the engine developed enough power to run on the idle
circuit, and I climbed up a 500 foot grade three times, wondering why
the throttle response was so poor.

The motorcycle ran a lot better when I sprayed some B-12 onto the
slide, freeing it.

 

Hey B-12,

The idle jets (and everything for that matter) that are in the carb now
are what was in it, #35's. I havent touched the floats, but the fluid
level is about 5mm short of the base. While this isn't optimum I don't
imagine it would be bogging the bike down.

I've had the carbs apart a million times to try to remedy this but it
could be possible the transition ports are still plugged. I've tried a
toothbrush, I've tried a twist tie, carb cleaner and brake cleaner,
compressed air, but I dunno what else to do with it.

Although, I did read a similar post on an HD forum about someone using
a CVK40, he put the needle jet holder in the wrong way so the needle
couldn't seat right and it was causing the bike to bog because of too
much fuel. I had a similar problem in that it was running way too rich
and that was because I had installled the needle into the spring seat
instead of needle first, spring seat second. So to whoever recommended
looking closely at the parts diagrams, thank you, it DOES help the
novice

 

oldgeezer wrote:

The only other thing I did to it was fix the ignition wire boot. I had
replaced the spark plugs a while ago and the brass connector in the
ignition wire boot had come undone, leaving me running on one cylinder
till I got it home. I fixed the boot (I believe the order went spring -
resistor - brass fitting) and while I was there I hauled off the carb
because I was looking for an excuse to, I had bought a rejet kit the
week before.

I dont think it would be a problem with the ignition wire, unless I put
the resistor in the wrong way. But if I did wouldn't it be giving off a
weak spark, or no spark at all on that cylinder? I've tried pulling the
plug on one cylinder at a time to see if one specific carb was causing
the problem, because my bike ran very well on one cylinder, but both
seem to be affected.

Other then that, thats all I had done to it.

 

Since the tolerance for setting floats is plus or minus ONE millimeter,
a fuel level that is
FIVE millimeters too low would make the venturi's job of lifting fuel
out of the float bowl
impossible.

Are you sure that the floats are installed the right way up? When you
remove them, look for a tiny witness mark on the tang that operates the
float valve. If you see the tiny witness mark on both sides, you may
have had the flats installed upside dow, shutting off the gasoline
prematurely.

You need some sort of depth gauge to accurately check float height. You
can buy a cheap plastic caliper if you don't already have a good
quality machinist's caliper made of metal.

I understand your that your complaint is that you start the engine and
it idles just fine and warms up, but when you open the throttle, the
engine dies. That's NOT bogging.

Most riders don't realize that there's a difference between bogging
down and an engine that's starving for fuel air mixture. It's almost
impossible for a CV carburetor that's set up correctly to raise the
slide enough so the engine will bog because the rider opened the
throttle too much.

Riders were able to do this with the older style slide valve
carburetors because the slide was pulled open directly by the throttle
cable. The rider would give the engine too much throttle and it would
suck in a huge gulp of gasoline that it couldn't burn and that unburnt
gasoline would be ejected out the exhaust pipe.

The CV carburetor takes direct control of the slide away from the
rider, and it won't allow a large flow of gasoline into the mixing
chamber if there isn't a corresponding large flow of air as sensed by
the diaphragm.

Ultrasonic cleaning might be necessary if you can't get carburetor
cleaner to squirt out of all three transition ports and the idle
mixture port. The idle mixture system gets air through the pilot air
jet (which may be in the carburetor inlet bell, or under the diaphragm
cap). The idle mixture system gets gasoline from the the idle jet in
the float bowl.

The pilot air and the idle gasoline mix, and then the passages split to
go out the transition ports and the idle mixture port.

If you have the carbs off the engine, block the throttle butterflies
closed, cover the idle mixture port with one finger and the pilot air
inlet with another finger, and squirt carburetor cleaner through the
idle jet. The carb cleaner must squirt out of the three transition
ports. If it doesn't, they are plugged up.

If you install the spring seat and then the needle, the carburetor will
come onto the main jet too early and the mixture will be far too rich
for the amount of air passing through the carb. The engine will blubber
and fire every other stroke. This is called "8-stroking".

 

I should have written:

"If you have the carbs off the engine, block the throttle butterflies
OPEN"

 

schreef:

So it looks like the carburettor after all.
Since the bike ran (until now), I doubt clogging. Furthermore, you have
two carburettors (I think). If one was clogged, the bike would pick up
at least on one cilinder.

Suppose it is a 'common' (both cilinders) problem:
What about fuel cap vent? Start without a cap on the fuel
tank and try the engine. (Don't smoke).
Is there any common fuel filter dirty (petcock)?
Vacuum hose to petcock okay?
Air filters? (They both get dirty at the same time).

Another common thing: you may have assembled both carbs
incorrect. Here are some things I can think of:
Have a look at the top end (diaphragm). The spring seat has kinda
5 fingers. The spring seat can be rotated. One of the fingers may
block the hole at the bottom of the vacuum piston. You could
have blocked that hole. Remedy, rotate the spring seat .

The needle jet goes into the body with the smaller
diameter first (carburettor upside down). Could be you did that wrong.

Fuel level can be measured as follows: You need the petcock be
open (has this bike a PRI position on the petcock? If not,
you gotta suck the vacuum line).

Take a piece of clear plastic tube that will fit on the carb drain
plug.
Set the bike so that carbs ar horizontal (need a jack for that).
Hold the tube alongside the carb body pointing up.
Open petcock (PRI or suck vacuum).
Open drain carb screw. Wait until fuel level settles in
tube. Do not lower and raise the tube, just keep it steady.
If you wiggled the tube, close drain screw, empty the tube
and retry.
As far as I know, fuel level must be 0.5 +- 1 mm above the
bottom edge of the carb body (the lowest split_casing line
of the carb).

Rob.

 

Yip, thats what happened to mine.

( air is pumped out diaphragm chamber ? )

 

I suppose that problem could be cured by silicone rubber cement.

Plug the hole(s) in the slide and try to raise it with your fingertip.

The Dynojet kits and the Factory Pro kits usually include a drill for
enlargening the holes so the slide will lift quicker as air is pumped
out from above the rubber diaphragm.

Enlargening the holes too much will cause the slides to fly up too
quickly on acceleration and drop too rapidly on deceleration. Throttle
control suffers...

 

As you are naturally careful in handling the slide assembly, it is not easy
to spot that they are pulling apart as the return spring 're assembles' them
before they are removed for inspection. I lightly centre popped them and it
seems to work fine.





The slide rising is a product of depression bled through from the intake,
but I was being petty, I wish I had not posted it. The idea here is to try
to assist not score points, I apologise.

 

matt,

Is there any chance you reversed the main and pilot jets when you put
the carbs back together? I vaguely remember the jets have the same
outside diameter at the base, but I'm not sure about the threads. Just
a thought.

Manjo

 

Vacuum cannot lift anything, the slide is not sucked upwards by vacuum.

Engine vacuum sucks most of the air out of the diaphragm chamber
through the hole(s)
in the slide.

Air at near-ambient pressure enters the oval hole in the intake bell of
the carb, and lifts the slide, overcoming light spring pressure and the
friction and weight of the slide.

Depending on the condition of the air filter element and the fact that
the intake air is in motion, this pressure may be around 0.25 pounds
less than ambient pressure.