I hate carburators!

I hate carburators, I have always hated carburators, and I probably always will hate carburators.

1979 KZ1000ST
4 into 1 exhaust, Kerker style but no emblem.
Individual pod air filters.
Valves clearances set. New spark plugs. Good compression.
Stock carbs, not sure what exactly they are but they do have an acc pump. Thoroughly cleaned and kits installed.
110 mains
15 pilot jets

Needle valve c-clip set on second to bottom, idle too rich even with set air mixture screws all the way in, but otherwise runs ok.

Moved c-clip to center position. Idles great with mixture screws about 3/4 turn out but coming off idle (like rolling out of a corner) leans out until into the throttle about 3000 rpm.

Went to 120 pilot jets to attempt to clean up the low range but now too rich at idle, even with mixture screws all the way in.

Not sure what to do next? Move c=clip on needles up one more?

Any advise will be appreciated. Thanks in advance.


Fugitive.

try 112.5 main,17.5 pilot,raise needle 1 from stock (middle)

What pods are you using ?

The pods do not have any markings on them. They look like K and N filters, but probably are knock offs.

Are the air filters clean and lightly oiled? Many guys over oil the air filters causing an endless search for problems to solve.

You might be a candidate for the "Wired George" ignition coil relay modification. www.wgcarbs.com is his website. He lists parts and how to wire the older Kawasaki's. The mod improves the primary side voltage to the coils producing a hot,fat, spark for improved combustion efficiencies.

To check the coils for low voltage, remove the tank, and with the ignition turned on check the input voltages at the coils. If it's less than battery voltage you have a voltage drop robbing the coils of full output and weak spark.

One guy here did the modification and had to crank down the idle 500 rpm's due to the bike running like new.

Fugitive wrote:

Any advise will be appreciated. Thanks in advance.

Get a stock airbox, it might save you a lot of misery.

Went to 120 pilot jets (?) to attempt to clean up the low range but now too rich at idle, even with mixture screws all the way in.

120 would be a main jet. Increasing the main jets can't possibly fix a low range problem. They work most at 3/4 - full throttle at RPM range from about 1/2 (redline) up to redline. If it pulls strong in that range, the mains are correct.

Pilot jet size, needle position, and even fuel level in bowls influence the low range running and throttle response. The diameter and taper on the needles is designed for the flow set by the stock headers and airbox. Change that and the taper doesn't match. usually you can jet in headers, pod filters are known for being difficult to get to match the needles.

Fugitive wrote:

...1979 KZ1000ST
4 into 1 exhaust, Kerker style but no emblem.
Individual pod air filters.
Valves clearances set. New spark plugs. Good compression.
Stock carbs, not sure what exactly they are but they do have an acc pump. Thoroughly cleaned and kits installed.
110 mains
15 pilot jets

Needle valve c-clip set on second to bottom, idle too rich even with set air mixture screws all the way in, but otherwise runs ok.

Moved c-clip to center position. Idles great with mixture screws about 3/4 turn out but coming off idle (like rolling out of a corner) leans out until into the throttle about 3000 rpm.

Went to 120 pilot jets to attempt to clean up the low range but now too rich at idle, even with mixture screws all the way in.

Not sure what to do next? Move c=clip on needles up one more?

Any advise will be appreciated....

Good advice from MFolks and bountyhunter.

FSM for 1979 KZ1000-A3/D2 shows Mik VM28SS, side located pilot air screw (1.25 +/-.25 turns out from lightly seated), 105R main jet, 15 pilot jet, 5SCN15-3 jet needle (middle clip), O-1 needle jet, service fuel level 4mm +/- 1mm (from edge of carb body to fuel level).
1979 KZ1000ST might possibly be different.

Reported history includes compression okay, but nothing about spark quality, ignition timing, advancer function, fuel level, whether pod air filters are clean and allowing adequate air supply, or choke plungers properly closing and sealing.

Side located pilot air screw governs amount of air allowed into pilot circuit. Turns in for richer, out for leaner. All the way in allows zero air for max richness. Only 3/4 out is still too rich. Pilot air passage may require further cleaning.

Clip position or main jet size has negligible effect on pilot circuit.

Good Luck!

stock jets for kz1000st are 110

I presume that the carbs on the bike came with it. But let's for an instant say you are not sure. Here is the story. If the pilot screws are at the bottom of the carb next to the float bole, they are fuel screws and lean out the mixture as you screw them in, and richen the mixture as you screw them out. Now, if you have stock carbs, these screws are on the side of the carb. These are AIR screws and work exactly opposite. These screws make the idle richer as you screw them in. These MUST be open to some degree at all time. They should be open anywhere between ONE (1) turn minimum to TWO & one eighth turns MAXIMUM. My guess Since I do not have a manual for your bike) would be about ONE & FIVE EIGHTHS open from lightly seated. They however could be clogged with corrosion or road grime (since they get air from the pilot air jet) and you may have to take them out and blow carburetor cleaner and then air threw them. These carbs are very simple and easy to adjust. The rule of thumb for main jet seizing is to; One size larger automatically from factory because they were already too lean in 1979 (you may go two sizes and you won't hurt anything. One size larger for POD filters. One size larger for a header. One size larger if you live at close to sea level. One size SMALLER if you live in the mountains. DON'T mess with the JET NEEDLE from stock. This will affect your mid range and knock the slats out of your gas millage. You should not have to mess with your Pilot jet from stock, but MAY go up ONE size. But since you are running too rich with the AIR needle all the way in, this is telling me that your pilot jet is more than big enough. If you are running any enhancements as mentioned before, (IE header, pods, etc) bring (turn) IN the AIR needle 1/8 (ONE EIGHTH)of a turn (FROM FACTORY SETTING) for each one. In other words the exact opposite as you would do with your main jet. I hope this helps. These carbs SHOULD be identical as on my Z1-Rs so I am going from that experience of 30 years.

Otto

Otto

now too rich at idle, even with mixture screws all the way in.

Patton hit it on the nose on this one.... Of course it's going to be rich.....

We all hate carbies but that's mostly because we don't understand them... Thus we must LEARN them....

Colortune is in order here..... :laugh:

OMR

Thanks guys for all the advice. I did notice that the spark looks wimpy and I'm going to check the power to the Accel coils. I will also double check the pilot channels to verify they are not blocked. Sounds like its time to get back to work. Thanks again.

Fugitive.

First thing, go to wgcarbs.com and look at the COIL REPOWERING mod under wg's Tech Stuff Index. Measuring the coil voltage is the first step. Second, the specs for a shafty carburetor assembly:

Mik VM28SS ID 1098
Service Fuel Level 4mm
Main jet #102.5
Jet needle 5CN17-3
Needle jet 258 O-4
Slide Cutaway 2.0
Pilot jet #15
Air Screw 1 1/4 turns out from lightly seated

First thing, check coil voltages, Next, turn air screws out to 1 1/4 turns out from seated and third (!!!!!) never oil paper element air filters (like yours).

Remove #4 pod air filter and twist throttle while the bike is parked on center stand and not running. Do you see gas squirt out of the accelerator pump squirter into the venturi? If not, clean the accelerator pump circuit because jetting will change if the thing isn't working.

If the pump IS working, go with #115 main jets, #20 pilot jets (IF YOU HAVE REAL GOOD SPARK - SEE COIL REPOWERING TIP) and reclip the jet needles to 4th slot. Slots are numbered 1 - 5 from top to bottom. You will need to resync carbs AFTER pulling out the slides as the M5 bolts holding the slide actuators to the slide rod change tension when you retighten them and sync will be out of whack.

Once you get the bike idling, turn air screws in/out about 1/2 turn to try and achieve max idle. Keep an ear open to idle change as the tach isn't very accurate at lower rpm. If no idle change occurs, don't be concerned as the air screws don't effect the air/fuel mixture a ton and just leave the screw at 1 1/4 turns out. Turn screws in and you richen and out and you lean as more air is allowed into the pilot passageway.

Oh yeah, nice bike... here is my 79: