High idle - 83 kz750

[bobcharles]

If ya'll remember my previous thread, I have my bike (mostly) running.
Right now I am having one hell of a time with a high idle. When the bike has run for a bit, and reaches what I assume is normal operating temps, the idle refuses to come down from 3k. Occasionally, a quick snap to full throttle then letting go will settle it down, but doing a mid throttle then going back to idle will have it humming high.
It really sounded like a vacuum leak, so I sprayed pretty much an entire can of carb cleaner around every hose and fitting, and the idle never changed.

It really lacks power at the lower RPM range, I have to give it a hefty amount of throttle to get it going, even if the clutch is slipping, but above 4k it comes alive very nicely.
So I think maybe my pilots are clogged, and was previously suggested to me. I cleaned and cleaned, rebuilt the carbs six times, the problem is always very consistant.

Looking at the spark plugs shows me the bike is running on the rich side; the plugs are sooty and black, but are not fouling out, I think anyways.

I noticed when the engine is warming, the idle will be a little higher when the bike is leaning on its kickstand, standing the bike straight or leaning to the right will result in a lower idle. This one is baffling me... made me think floats, but they all check out when I test them according to the service manual.

Also, while the engine is warming, choking will result in odd behavior. Rather than racing up to around 4k RPM like I'm used to, it'll chug around 2k at start up, and dip to around shortly after. Then as things heat up, it'll climb. When fully hot, it'll choke over 5k. Throttle response while cool and choked is excellent.

Attempting to run without choke results in instant death if cool, and terrible throttle response if I can keep it from dying by snapping the throttle. As things warm up, it takes longer to die from an idle. Eventually it'll run without choke, but only after 10-15 minutes. Throttle response isn't bad, but it could be better. Then as previously stated, it won't want to come down from 3k.

It's rideable... but it wants to die so bad when trying to take off from a stop. It's rather unsafe if traffic is bad and I need to get around a turn or intersection in a hurry.

Do I need new pilot jets? Internal carb damage/leaking?

[MFolks]

Check the float levels and look for a vacuum leak(spray some carb cleaner around the carb boots and fittings and see if the rpm's go up. If they do then the leaks nearby). Another place to look at is the vacuum ports used for carb sync. as they will crack and leak . Carb boots will crack and leak. Look at the choke mechanism as this sometimes has one or more carbs at partial choke.

Have you sync. the carbs lately and had the valve adjustment checked?

Just a few places to check.

[StarGate]

Have you checked to see if the throttle cable is binding? With the engine off and full throttle, release the throttle and see if it snaps back idle position.

[OKC_Kent]

If he has CV carbs would a bad diaphragm cause those symptoms?

[antiq]

When you cleaned the carbs did you check the diaphragms? No tears or holes? Make sure the slides move free? Is the airbox hooked up? No airbox and stock jets will give you what you have. Very lean idle jet range, slow response,and rough transition to the main jets.

[bobcharles]

The diaphragms are intact, I triple checked each one carefully for holes and tears. The slides move easily... no rough spots where they'd stick.

cable is moving freely, I've watched the butterflies and cable when I work the throttle.

I rode just not long ago coming home on a cool night, and it was behaving worse than during the day when it was warm. From start, with choke, it was at a 'normal' idle, only around 1200 ish. Still had nice response, and working it up to 4k made it stay there. Let it idle for a minute like that, then dechoked.
promptly tried to die, but I worked it back up manually keeping the RPM around 2k.
I also don't know if I mentioned it in my first post, but I have the idle speed adjustment backed out all the way - it's not even touching the notch on the throttle control. PUtting it in, even a little bit, makes the high idle problem, obviously, significantly worse.

Rode like that the entire way home. It's really lacking power, it feels like I'm driving a 250cc bike. WOT in first gear didn't really do a whole lot.

Also backfired twice when coming down from a high RPM - about 6k I think.



Also, I do not know how I forgot to mention this, but the outside pipes are significantly cooler than the inside ones. I thought it was due to increased airflow, but it's just too big of a difference, I think, when its not moving.
The inner pipes can be hot where you can feel the heat from inches away, and they're making the frame in front of them warm, while the outer ones you can almost touch them. They'll still burn you if you touch them (as I accidently did), though. There's also a difference in cylinders 1 and 4. Cylinder 1 is usually cooler than 4.

First thing I checked was spark, and they're sparking fine. Nice blue sparks on both plugs.

I am thinking the carbs are so unbalanced that the inner two are doing most of the work?

But then it doesn't explain the racing hot idle. I am so confused with this thing. I wish I could pay someone to show me what to do. Don't really want to take it to a shop, since they likely won't let me sit there the whole day and watch...

[gpzrocker]

Valve clearances checked,as per MFolks?

And how did you clean/rebuild the carbs, a little more detail there. Did you take the floats off 6 times without breaking a tang? Impressive. Or I am just not that lucky?!

And as Antiq said, are you running the stock airbox? Those boots must have been replaced sometime, or you would be cursing the very day they were invented time and time again.

My mechanic lets me sit in on my bike work. I redid the carbs twice and it ran good: he tsked me and spent two hours polishing and cleaning and it was amazing the difference.

Have you really pulled the floats off 6 times??!!

[StarGate]

It sounds a lot like mine did after a breakdown followed by extended storage many years ago. It mostly ran on 2 cylinders, would constantly hang at 4k rpm or just jump up to 4k from idle all by it's self. I put new coils on when I noticed the spark was weak but that didn't fix anything. Turned out to be 3 things I did that fixed all that. I did the coil power rewire mod, put new manifolds on, cleaned the carbs after letting the bodies soak in berrymans carb dip. That took care of mine.

[bobcharles]

I checked out that voltage mod, it sounds good. I get about 11.2 volts to both coils, so it might help.

I have new manifold and airbox boots, so I know they're good. I was careful during installation not to tear them. Yes, I am running the stock airbox. Everything about the bike is stock.

My carb cleaning involved removing everything from the carbs, while still leaving the carbs attached as a unit. Soaked the jets in some B-12 cleaner, while I went to work on the passages with carb cleaner and some air in a can. Perhaps I should try soaking the carb bodies?

I've never broken, or even so much as bent, a tang when cleaning my carbs. Not really sure how you'd break it; it's not like the float valve is so hard to remove that it'd bend the tang?

I have not checked my valve clearances yet. The engine doesn't have many miles on it, so I really hope they've not gone out of spec. I will probably check the clearances sometime soon.

Also, on the coil mod, since I have two coils, I would need to run two relays, one per coil yes?

[StarGate]

No, only takes one relay to do the job. You run the power out of the relay and split it to run to both coils.

[bobcharles]

When running it to both coils off the same relay output... won't that cause all four plugs to spark at the same time? Or are they ground switched?

[MFolks]

On the four cylinder Kawasaki engine you have two ignition coils usually set up to fire plugs #1 and #4 (viewed from the seat) and #2 and #3 reading left to right. The coils have two ignition leads to the sparkplugs and will have what is called a "wasted spark" because one cylinder is on the exhaust stroke while the other cylinder is on the power stroke or combustion cycle.

[bobcharles]

yea, I know about waste spark systems. I'm very familiar around fuel injected cars, but carbureted motorcycles are a new beast to me.

I misread the website, I thought the relay was getting a signal from the ignitor, which didn't make much sense to me. The one Stargate posted clarified it for me. I need to learn to read better, haha.

[StarGate]

To answer the first question, yes they are ground switched.