Finally got my KZ400 to start! But........

Hello guys, Everybody has been a great help here. I really appreciate that. So I just installed my new mikunis VM30's and it starts. But the problem is, if I do not give it any throttle the bike shuts off. Carbs are clean cause they are new. I changed the fuel. What else can it be?

Have you tried increasing the idle stop?

Hello kyan44

What do you mean with when you say "my new mikunis VM30's"? Have you rebuild them by your self?

Are the carburetors synchronized?
Intake boots with no air leaks?
Float bowl high correct?
Air screws set to reference?
Air filter and housing stock or K&N?
Ignition timing ok, correct gap on pointer(dwell)?

Get the full services and repair manual

www.manualedereparatie.info/manuale/Kawa...dereparatie.info.zip

I haven't synchronized it yet. That's what I was trying to do. For the intake boots, how do I check for air leaks? How do increase idle stop?

Spray brake cleaner on the intake boots. If the engine revs different as usual (mostly lower) you have an air leak there.



Pic´s are out of th service manual in my first posting. Get it.

VM30s will work on the KZ400 but they are far from plug-n-play even if you bought them "pre jetted for the KZ400" from somewhere. Different altitudes, wear on the engine resulting in performance differences, etc. will create differences between 2 exact same bikes. I may use 25 pilots, 230 mains, the stock needle jet and jet needle and the needle set on the middle position with a 2.5 throttle valve but someone else may have better luck with 30 pilots, 190 mains, needle set one clip up with 2.0 throttle valves. You'll have to tune those carbs to your bike - which is one of the downsides of going to Mikunis rather than using the stock carbs. The stock carbs are a little more forgiving one they are cleaned and working well, assuming the stock airbox and a sufficient exhaust setup is being used. However the benefit of the Mikunis are that parts are much more available and tuning them is a fairly simple process - just follow the steps.

There are a lot of guides for tuning Mikuni carbs, just do some searching. You may find some stuff here on KZrider, but I know there is a lot of information on the Do The Ton forums. Here is a pretty simple description that I found quickly: www.mikunioz.com/tuning-tips-and-manual-downloads/ - The attached pic is a good starting place to show where each of the systems come into play.

It's a good sign that it starts up easily - I assume you are starting it with the chokes on and then turned them off at some point. If you've gotten that far then you'll be able to figure out the rest. Leave the chokes on until the bike starts to stumble. After that you ought to be able to turn them off and retain an idle or you may need to go to partial choke. If you go to partial choke then let it run like that until it starts to stumble again and then turn the chokes off. Ideally it should idle at that point as long as you want. It can help during initial tuning and when adjusting your mixture screws to set the idle higher. After it has idled and warmed up a bit then you should be able to start rolling on the throttle a bit and back off.

I don't remember where I found this but it helped me quite a bit. Between this and the information that I linked to above it should give you a good place to start:

To properly tune the VM's it's critical you get the Pilot and air mixture set properly at idle before you do anything else. you'll need a box of fresh plugs to do this properly...at least 3 or 4 sets.

1st get the carbs properly synched both cables and slide idle stop screw (see below).
2nd ride the bike around for 10 minutes or so to get it fully warmed up. then set the idle mixture screw (see below)
3rd Now that the bike is warmed up install new plugs and start the bike WITHOUT ANY CHOKE OR OPENING THE THROTTLE AT ALL. Let the motor run for 3 or 4 minutes like this at idle NEVER TOUCHING THE THROTTLE. Then pull the plugs. The plugs should be very light tan at the base of the porcelin cone and white at the tip. You'll probably need to get a range of pilot jet sizes. repeat this test with NEW PLUGS EACH TIME until you get the proper plug readings. if you want to save money on plugs, start with the leanest pilot jets first...they won't color the plugs and will let you reuse the plugs till you get a reading on them

Two Mikuni round slide carbs are simple to balance and syncronize perfectly with no carb sticks or other vacuum guages.

Insert the smooth end of a drill bit from the intake side under the slide throttle valve cutaway and set the idle thumb screw so that it just drags on the smooth end of the drill bit. Use the same drill bit on the other carb and set it the same as the first. If the motor idles too high, use the next smaller bit, or if it idles to low use the next larger drill bit etc. Do not do this with the motor running.
Once both idle positions are set, you can easily set the slides to lift together at the exact same time, and be at identical slide position heights by using two popcicle sticks. Put one popcicle stick into each carb about the same distance under the slide then simply twist the throttle and watch when each popcicle stick begins to move. Now adjust the throttle cable adjusters on the top of the carbs so that you can see both popcicle sticks begin to move at exactly the same time.

Turn up the idle to about 2000 RPM. Turn both idle-air screws all the way in and back both out 1 1/4 turns. Screwing it out will lean the mixture while screwing it in will richen it. Adjust the jets until you have the best idle. If turning the screw between one and two and a half doesn't have any affect, the pilot jet will have to be replaced with either a larger or smaller one. If you have to set the screw to less than a turn out then you'll need a larger pilot jet. If you have to turn the screw out 3 turns or more then you'll need a smaller pilot jet. While adjusting the pilot screw, turn it 1/4 turn at a time and test run the bike between adjustments. Set the idle back down to normal range - around 1000 RPM. Adjust the pilot circuit until the motorcycle runs cleanly off of idle with no hesitations or bogs.

With a clean set of plugs in there, start the bike. Let it warm up but don't hold open the throttle in any way. You're checking idle-air mixture only here. After you've let it run at idle for a few minutes, turn off the motor and pull the plugs - fouled = open the idle air screws up another 1/2 turn, white = turn them in 1/4 turn. Repeat with fresh sets of plugs until they look white at the tip and tan at the base of the porcelin

After you get the pilots set you can work on the mains and lastly the needles. You can do this by marking 0, 1/4, 1/2. 3/4, and full throttle with tape on your throttle and doing throttle chops at each setting. Adjust the proper jet system based on the photo showing systems vs throttle position.

Ok I finally got it started to run, rode it around the block. I had to adjust the idle screw. I'm guessing both of the idle is in sync now that it starts. But the RPM shoots up pretty high, like 4000 almost 5000 RPM. What could that mean?

have you sprayed the intake boots with brake cleaner?
its sounds you have some air leaks and carbs are not adjusted right.
can you adjust to 1000 - 1200 RPM or stop the engine before???

So today I did some adjustments to my carbs. Started up fine at first. Then adjusted again. It was a bit hard to start. But it ran for a bit. Turned it off checked the sparks plug. And it was black. So its too rich. Put thr plugs back in and tried to start it again. But this time there is a reallyloud bang coming from the exhaust or engine. Almost like a gun being fired. Now it is not starting. Is it backfire? Should I be worried?

If it is running that rich there is probably a lot of unburned fuel passing through the exhaust. My guess is that it was some of that that ignited and caused your loud sound. Give it a few minutes and then try again.

Did you start it with the chokes on? If so were you able to take the chokes off and then it still idled?

If you were able to start it without the chokes on (assuming it is not hot out where you live) then your pilot jet circuit is way too rich. If you started it with choke and then turned them off and let it idle for awhile and your plugs are that sooty then your pilot jet circuit is way too rich. If you never got to the point where you could take the chokes off and it would idle then your pilot circuit may be too lean. Try adjusting out the air/fuel mixture screws a half turn at a time and checking your plugs again. If you get far enough that opening/closing them up more does not make a difference or you get under 1 turn or past 3 turns out then you'll need to go to larger/smaller pilot jets and try the air mixture screw adjusting again.

You will probably need to swap in another set of plugs if they are really sooty or fuel fouled though you may be able to clean them off.

One other question: are the plugs black and sooty, black and sooty and soaked with fuel, or black and oily?

your spark plugs are like short cut internally by fuel, the spark goes the shorter way over the "wet" insulator and sometimes the regular (spark gap) with a loud bang.
In this case i do a little dirty trick.
Try to heat up the spark plugs with a gas torch to dry and burn out the fuel.

So that loud bang is somewhat normal? No need to worry? But my sparks plug is black and sooty. So it rich for sure. Would I need a bigger pilot jet?