1980 kz750 ltd idle problem

I have checked all vacum tubes, all carburetor gasgets and made sure the throttle cable was at the lowest setting but not loose
when I start it up it goes straight to 5,000 rpm and i shut off immediately.
I went to my manual and I adjusted the throttle screws on top of each carb but the directions where very vague "tighten until fits snug then reverse 2 rotations" does that mean all the way down then two back or until it gets hard to screw down and two back?
when I adjusted them either way it started at 1,000 for a minute then shot up to 5,000.
I dont want to take it to a shop but I dread I will have too.
any suggestions would really help

Did the reported issue occur spontaneously, or after some sort of carb work was attempted (such as, for example, attempting to sync the throttle butterflies)?

One of several possible conditions that might cause a racing idle could be an air leak, which might result from a loose clamp that secures carbs to carb holders, or some other air leak source. Other possibilities include a hanging throttle mechanism (for whatever reason), failure of throttle slide to fully close (for whatever reason), etc.

With regard to the pilot adjustment screw, many service manuals say "X turns out from lightly seated" with caution against over-tightening the screw. However, I don't suspect the excessive revving in this case to be resolved by finer tuning of the pilot screws.

If not already done, could check out the manual available via this link (scroll down and click on "The Bible."
kz.bike-night.com/

Good Fortune!

pappy750 wrote: ................
I went to my manual and I adjusted the throttle screws on top of each carb but the directions where very vague "tighten until fits snug then reverse 2 rotations" does that mean all the way down then two back or until it gets hard to screw down and two back?

The screws at top front on the carbs are the pilot mix screws and like Patton said adjustments here wont cause the issues you are seeing. If you are playing with them then the stock setting is to screw down until LIGHTLY SEATED and back out 2 turns

This had happened to me but only when I forgot to tighten the hose clamps on the rubber carb boots between carb and engine.
Lie Patton said some history would help.

Stay away from a shop !!

Im just not too sure what "seats lightly' means :huh:
all boots leading to the carb from the airbox is secure
all boots leading to the motor from the carb is secure
throttle cable adjustment is fine

I Have been working on this for a couple of weeks and I really need to just ride it, Im having rough times in my life and its something I need to do. so if I cant fix it I will have to take it to a shop, I need it to run. :dry:

this was a project bike I started so this is the first times I have cranked it myself.

If still fitted, the stock clean-air paraphernalia includes hoses and fittings which are possible air leak sources.

Any unplugged vacuum nipple(s)?

Any split or cracked hose that's attached to any vacuum nipple (whereby outside air is being sucked into the hose)?

The pointed end of the pilot adjustment screw is delicate.
The tapered point moves inside a small orifice inside the carb.
If the screw is overly tightened, the point may be damaged or broken off inside the orifice.
Lightly seated means not overly tightened.
Keep Godzilla away from the screw.

The cracks allowing air leaks through an old worn-out carb holder may be virtually imperceptible. Hence reason for the test method of spraying with WD40 and noting any effect on rpm and/or smoking from exhaust.

Racing idle is a classic symptom of an air leak.
Worn-out or damaged carb holders and/or loose clamp connections to carbs are classic causes of air leaks.

Good Fortune!

What may also help is if you say where you are so you might get some assistance from a local member. Check everything you can think of that can lead to an air leak as Patton said. Good luck

i just went through all the tubes, no luck
my friend that actually races 600cc class motocross has his own mechanic that is going to take a look at it in the next few days.
the friend of mine drives like a bat out of hell and breaks a lot of things so I know this guy is top of the line.

is it bad to let it stay at 5,000 for too long btw? i could maybe find the leaks the wd40 way it just scares the heck out of me when it roars up like that, I feel like its going to explode :huh: :blush:

If there's no sign of air leaks and vacuum nipples are good and throttle cable is not hanging up then the only thing I can think of is something wrong with the mechanical operation of the throttle flaps/ butterflies. To investigate that you'd need to take the carbs off and make sure the flaps are all down (butterflies closed) when the throttle mechanism is at rest. And give the whole operation of opening and closing the throttle a good inspection

I had a racing idle problem and it was the carb holders. Spray carb cleaner anywhere around them and the idle jumped, replaced those and the problem went away. How about the petcock? check that?

I'll test for leaks
but how long of intervals should I allow it to run at 5,000? isnt that bad for my engine to stay at such high revs in neutral ? I dont want to damage it and cost myself more money by running it too long so im not going to work on it until I can find an answer.
thanks everyone for the help ill be searching the web some more about how long i can keep it up there and keep looking at replies on here for advice as well.

Don't let it run at 5,000 rpm at all! And don't bother checking for leaks at that high rpm as it won't tell you much. Do you have the vacuum caps on and are they tight? If not, replace them; otherwise -

First - Unhook you throttle cables at the carbs and start the bike to see if it jumps to that high rpm; if it does - shut it off. If it doesn't you have a cable / throttle issue to fix.

If it runs at high rpm with the throttle cables unhooked examine the throttle stop (this is where the idle adjustment knob is) and turn in counter clockwise to reduce the idle - if need be try to manually close the throttle at the carbs. If you turn it all the way out and the idle still jumps when you start the bike your slides are probably sticking open and you will need to examine the carbs to find the problem. Ed

pappy750 wrote: ...when I adjusted them either way it started at 1,000 for a minute then shot up to 5,000....

When first starting the engine without ever touching the throttle grip, there may be sufficient time at the lower rpm (before the rpm jumps higher) to spray WD40 over the carb holders and watch for exhaust smoke (caused by ingestion of WD40).
A change in rpm might also result from ingestion of WD40, but might not be as noticeable as the exhaust smoke.

During the entire test procedure, NEVER TOUCH THE THROTTLE GRIP.
Because the slightest blipping of the throttle may incite the racing idle.

Good Fortune!