KZ550 cuts out

I picked up a 1982 Kawasaki KZ550 and have it running except it cuts
out whenever I apply more throttle. Today I tried a mountain road and
needed to open the throttle beyond normal and the engine started
running very rough, I lost speed and couldn't get it back. When on the
level I've had it up to 50MPH without problem but fast accelerations
cut out too.

I've put in new spark plugs, new gas, new fuel filter, new air filter,
new oil and filter. Does anybody have and ideas of how to fix it?

Thanks, G

 

Carb cleaner. Get some Berryman's liquid and follow the instructions.

pierce

 

I'm fairly sure your motorbike has an electronic ignition system. You
can look up the parts diagram on www.partsfish.com to see if it has
ignition contacts (points) or an ignition module and a signal generator
with pickup coils.

Your engine runs on the idle jets a lot of the time when you're just
cruising down the highway. You'd be amazed at how little throttle you
actually need to use. The idle jets and idle passages get gummed up
when the motorbike sits around unridden for a few months. Gummed up
jets and passages stop the flow of fuel to the engine when you open the
throttle and you'll hear the exhaust go "piffle-piffle-SNAP!" or even
"fart-BANG!"
as you roll the throttle off.

When the idle jets are plugged up, the engine is hard to start, takes a
long time to warm up, and acts very "cold blooded". It wheezes and dies
when you open the throttle.

The easy solution is to go down to Wal*Mart or any good auto parts
store and buy a 15 ounce can of Berryman's B-12 Choke and Carburetor
Cleaner. Add 3 or 4 ounces to a full tank of gasoline and go for a slow
ride. Watch for cars coming up behind you!

You want to ride slowly so the engine has to suck the mixture through
the idle jets. After several miles of running, the idle RPM will
increase and you will have to turn the master idle knob down. It may be
underneath the carbs or on top. It will probably be between the two
carbs on the right side of the engine as you sit on the motorbike.

 

Thanks for the reply. Yes it has an electronic ignition. However,
idle seems to work fine and slow speeds and slow acceleration work fine
too. The only problem is when I accelerate fast or climb a hill where
the throttle has to be open just a little bit more. Does your thoughts
still apply?
Thanks,
G

 

Pretty much. I figure it's the carburetors or the fuel supply. Not much
ever goes wrong with the electronic ignition system, it either works or
it doesn't. Riders have been screwed up by ballast resistors in the
circuit feeding the ignition coils though. They don't realize that some
Kawasakis used a ballast resistor to drop the 12 volts from the battery
down to 6 volts so they could use a 6 volt coil and have a hot spark
for starting.
Then riders try replacing the 6 volt coils with 12 volt coils and get a
weak spark or they have a bad ballast resistor and get a weak spark
that way.

Another possibility is fuel starvation from one or more stuck float
valves in the carbs resulting in low fuel level. The B-12 will clean up
the float valves, if that's what it is.

There might also be crud in your gas tank. Rust and water build up over
time and cause lots of problems with the fuel supply system. Riders
find their gas tanks are so badly rusted inside they need to acid etch
the metal inside the tank and apply a plastic sealer to keep the tank
from rusting again. Kreem and POR-15 are popular sealers.


Check the parts diagrams at www.partsfish.com to see if there is a
filter inside the gas tank on the standpipe that feeds the petcock.
Some carburetors also have tiny wire screen fuel filters above the
float valve. Check the carburetor parts diagram to see if you have one
of those screens in your carbs.

It's also possible to have petcock problems. It's a gravity flow
system, and it doesn't take much to stop the flow. Some riders have
found that the air vent in their gas cap has plugged up and the
resulting vacuum in the gas tank stops fuel flow until they remove the
gas cap.

Typically, the petcock on most Japanese motorbikes is operated from
vacuum from one carburetor. The vacuum pulls on a diaphragm on the back
of the petcock, opening a little spring loaded valve. You can check the
diaphragm operation by removing the vacuum hose and the fuel hose that
goes to the carburetors. After a few drips, the gasoline hose should
stop dripping, indicating the automatic valve is sealing. When you
apply suction to the vacuum hose, fuel should start flowing.

If there is a leak in the vacuum hose, the automatic valve might not
open. The hose can be old and have splits near the ends where it
attaches to the carb and petcock, or it may have a split in the middle
that would drive you crazy trying to find what was wrong.

Once I had a kinked fuel hose that was blocking gasoline flow. The hose
was the wrong kind of hose, it wasn't meant for a motorcyle, it was a
thick-walled car fuel hose. It took me three weeks to figure out what
the problem was.

There will also be a PRI position on the petcock for priming the
carburetors when the float bowls have gone dry from the motorbike not
being ridden. When you put the petcock in the PRI position, you should
get a good flow of fuel without the engine running.

You might try selecting PRI when the apparent fuel starvation problem
happens.

I recommend loosening the screws that hold the selector lever onto the
petcock and operating the petcock slowly and carefully before using it
to select PRI while riding.

If the motorbike has sat unridden for any length of time, the selector
lever will stick to the rubber seal inside the petcock and the seal can
be ruined. They cost about $10 each and with special handling, a mail
order company may charge you $20 for that damned seal.

Then tighten the screws again when the petcock selector lever moves
freely. You can also remove the selector lever to clean rust and crud
out of the fout holes in the petcock, but nothing will stop all the
gasoline from coming out of the prime hole.

If you drain and remove the gas tank from the motorbike, you can take
the whole petcock off for cleaning. Be careful not to damage the oval
rubber seal between the petock and the gas tank. It could cost you
another $20, unless you buy the whole petcock rebuild kit.
www.oldbikebarn.com has petcock rebuild kits and carburetor rebuild
kits.

A lot of shade tree mechanics have gotten into the habit of thinking
that a carburetor rebuild kit is a "magic cure" for carburetor
problems. They think, "Oh, I'll just throw a kit into the carbs and my
problems will go away."

They are wrong. First, they have to understand the mystery of the
motorcycle carburetor, why it's built the way it is and what happens
when it screws up.

 

Thanks for the great reply. I finally broke down and removed the
carburetors to clean and adjust the float bowl and associated jets,
etc. Only one of the four carbs was clogged a bit. I felt confident
that cleaning it would help, but it didin't. I went through the
petcock and it's working great as described. I feel like you, that it
is a fuel starvation issue and expereince tells me I need more gas at
the time of acceleration. So, how do I get it? I thinking of drilling
out the jets. Would 85 octane gas cause the issue? I'm thinking of
draining the tank again and put in 91 octane. What do you think?
Previously I have replaced all the gas and vacuum hoses and inline fuel
filter. I don't have the little screen filter as you mentioned. Could
valve clearance adjustments make a difference?

 

Don't. You've got a problem with a (presumably) stock bike. The bike
didn't do this when it was new, so find out what's the issue before you
go making modifications to the thing. The more you change, the harder
(and more expensive) it will be to find the issue when it persists
through each change.

Don't. Unless you've modified the engine, fill with recommended octane.

3 most likely issues (IMO):
carbs still dirty (e.g. you missed a jet).
kinked fuel hose
fuel flow constrained

What sort of fuel hose did you use, and how did you route it? Does it
kink up (even partially) when everything's assembled? Things might look
good before you tighten down the tank, and be a bit constrained
afterwards. Automotive fuel hoses tend to be more rigid (and kink-prone)
than stuff made for motorcycles.

It's also possible (perhaps not likely, but possible) that the inline
filter is preventing enough fuel from flowing at higher rpms. If you're
confident that the fuel tank is clean, you might remove it and see if
that solves the problem.

There's other possibilities, but these are fairly easy to check and are
common issues. HTH

--
Later,
John



'indiana' is a 'nolnn' and 'hoosier' is a 'solkk'. Indiana doesn't solkk.

 

Maybe there is still crud up inside the idle mixture ports. If you have
CV carbs (the type with a round cap on top and rubber diaphragms that
operate the vacuum slides---my friend's 1982 GPZ-550 had CV carbs) the
EPA started installing anti-tamper plugs to conceal the idle mixture
screws.

The plugs will just be round and flat and they will be downstream of
the throttle butterflies, probably on top of the carbs just forward of
the diaphragm caps. In order to remove them, you carefully drill a
small pilot hole in the plug, then drill it just big enough so you can
screw a small sheet metal screw into the plug.

Then you can pull the screw out with a pair of pliers and the plug will
come with it. The next step is to turn the idle mixture screws all the
way clockwise until they just stop turning. Count the number of turns
for each carb's idle mixture screw and write it down.

The cylinders are number 1 to 4 from left to right as you sit on the
motorbike so you can number the carbs the same way. Then you can
carefully unscrew the idle mixture screws and remove them. There should
be a spring, tiny washer, and tiny rubber o-ring on each idle mixture
screw. If you don't find a rubber o-ring on an idle mixture screw, it's
probably stuck down in the hole.

Don't mix up the screws, you want to put them back where they came
from. With those screws out, you can squirt aerosol B-12 down the idle
mixture screw hole.

The best bet is to have the carbs off the motorbike so you can squirt
B-12 down the idle mixture screw holes. The carb cleaner should squirt
out through the idle jet, through the idle mixture discharge ports
(there should be three transition ports just downstream of the throttle
butterflies and the one port that's controlled by the idle mixture
screw). The carb cleaner should also squirt freely out the pilot air
jet in the carburetor bell mouth.

When you reinstall the idle mixture screws, just put each screw,
spring, washer, and o-ring in the hole it came out of, turn it
clockwise until it just stops turning, then turn it back out the same
number of turns you wrote down when you removed the screws.

If you want to adjust the mixture a little richer, turn the screws 1/4
or 1/2 turn counterclockwise. If you want to lean the mixture, turn the
screws 1/4 or 1/2 turn clockwise.

There is also the possibility that the float levels were adjusted
incorrectly by some previous owner. When the manual specifies that the
float level should be, say 15 millimeters from the gasket surface, that
gasket surface isn't the surface of the gasket that goes between the
carburetor body and the float bowl, it's the surface on the carburetor
body that the gasket goes against.

And floats are adjusted with the carbs sitting upside down on the
bench, with the adjustment tang of the floats just resting on the pin
that comes out of the float valve.

If the manual calls for the float level to be 15 mm plus or minus 1.0
millimeter, making the bottom of the float 14 mm from the gasket
surface *raises* the float level, making the idle mixture richer.
Making the bottom of the float 16mm will lean up the idle mixture
because the vacuum in the carb has to work harder to suck fuel out of
the float bowl.

No, don't do that, you'll just screw up the jets. They cost about $4 or
$5 each and they are drilled with incredible precision. Suppose you had
a #100 main jet. The diameter of the orifice in that jet is 1.0
millimeters, or 0.0394 inches. If you installed the next size larger
jet, a #102, the diameter of that jet would be 0.0402 inches. The
difference in diameter would be 0.000788 inches. Can you imagine trying
to find a drill that would do the job?

You definitely want to use 91 octane if the engine calls for it. 85
octane gasoline will preignite when the engine gets hot and you'll hear
a "pinging" noise that sounds like the valves are very loose. Pinging
takes place when the mixture in the cylinders ignites *before* the
spark plug fires. This raises pressure in the combustion chamber very
high and it can lead to detonation, where the mixture in the cylinder
explodes with a bang and pistons can be broken.

You can tell that an engine is pinging from lean mixture or advanced
timing or from overheating by the black specks burned onto the nose of
the spark plug insulator. The black specks look like pepper.

Other reasons for pinging are low octane gasoline and carbon buildup in
the combustion chamber. Glowing specks of carbon will light the mixture
off before the spark plug fires.

The next stage of pinging after the little black specks is when the top
of the aluminum piston gets so hot it starts melting. You'll see little
silver balls of aluminum on the spark plug.

The next step after that is when the top of the piston caves in from
melting. The spark plug is full of melted aluminum and there is a hole
in the piston. The piston might seize and break a connecting rod.

I have seen all of this happen to engines I've tinkered with.

The normal way valves wear is that the valve heads sink into the valve
seats. This takes up the tiny amount of clearance between the valve
stem and the shim or screw adjuster. When the clearance is gone, the
valves can't seat and the piston blows fresh mixture right back out the
intake port. The engine can run very lean and ping.

 

Drilling out the jets will cause you to have jets that are junk. Do it to
a pressed in jet and the carb is junk. Short version? >Don't do it.<
Want to stick someting in the jets? Try some musical instrument wire.

Look for evidence of a white powdery substance or brown powder. One n
aluminum oxide and the other it rust. Both are bad news but can be cleaned
out.

Are the slides (if equipped) free to move?

pierce

 

Guess what? I did not drill the jets but did check everything
mentioned here without success. Finally I removed the air filter and
it now works. I'm confused if it's a fuel starvation issue, why would
an air filter that isn't totally clean cause it to act this way? I'll
be buying a new air filter today and keep my fingers crossed it works
as well with one as without.

 

Do you have constant vacuum (CV) carbs, or slide valve carbs?

Looking at the carburetor parts diagrams on www.partsfish.com, I see
that the KZ550A1, KZ550A2, KZ550A3 had slide valve carburetors with
oval or square looking tops and throttle slides that go up and down as
you twist the throttle

The KZ550A4 had constant vacuum (diaphragm-type) carbs. Increasing
vacuum moves the slides up and down as your open the throttle
butterflies.

If your carbs have a big round cover on top, they are diaphragm-type
carbs and riders imagine that vacuum is what lifts the vacuum slides to
pull the jet needles out of the needle jets in order to richen up the
mid-range mixture.

Actually, it's *air* that gets past the air filter that lifts the
diaphragm from underneath when the air gets sucked out of the volume
underneath the diaphragm cover.

Your old plugged up air filter might not be passing enough air to lift
the vacuum slides.

I also notice that, regardless of whether the KZ550 had slide valve
carbs or CV carbs, there is an EPA anti-tamper plug concealing the idle
mixture screws. If you can't see any slot headed brass screw on the
sides of your carbs or in front of the diaphragm covers, the EPA plugs
are still there.

On slide valve carbs, you turn the idle mixture screw clockwise to
richen the idle mixture.

On CV carbs you turn the idle mixture screw counterclockwise to richen
the idle mixture.

If you have CV carbs, do the vacuum slides move up and down freely as
you twist the throttle? If you see one slide that doesn't move, it
might be stuck and a little bit of aerosol carburetor cleaner sprayed
on it will free it up.

But if it still doesn't move, the rubber diaphragm might be torn or
have a hole in it. A new diaphragm/slide assembly costs about $100.

 

My model is not an A but a C version. The carburetor on my cycle is
shown at:
http://www.powersportspro.com/partsfish/displayfiche.asp

I expect you're right that lack of air was the culprit. I just took a
38 mile ride without even a slight hicup in engine operation with the
new air filter. My old filter looked like it had some oil on it at one
time or another and even though I could see through it fine it must
have caused it to reduce air flow. When I got it the oil was about 2
quarts overfull and if they ran it that way it would have sucked up oil
into the air filter. So, maybe that's what happened.

I did drain out the 85 octane gas and put in 91 octane and the engine
is running much quieter. It must have been pinging.

No matter what, it's running like a new engine again at 20,000 miles.

 

The session was expired so I was back to square one.

It's a 1982 KZ550C3? If so, it has slide valve carbs and the pilot air
screw is concealed under the 92066 plug on the side of the carb. You
can help the throttle response by removing the plug and turning the
pilot air screw clockwise about 1/4 of a turn to make the idle mixture
richer. But a lot of shade tree tuners go crazy with their idle mixture
screws, turning them three turns in or out and that's far too much
tweaking.

If a paper filter gets oiled or water soaked, it's ruined, it won't
flow air. If you look at the air cleaner diagram for the KZ550C3,
you'll see a 92059D hose in the bottom of the airbox. It's probably a
blind hose that is like an appendix. It's probably supposed to catch
condensed oil vapors and the motorbike owner is supposed to somehow
magically
just *know* that the hose is supposed to be removed and drained
regularly.

Well, I'm sure glad that you're making some progress and can now enjoy
your KZ550.
They were one of the neatest middle weight motorbikes of that era.