Idle Speed Increases. Why??

If you have tried and eliminated all of the above, consider the following:

When the engine in cold it needs a richer mixture, therefore the need for a choke which in many KZ's is actually a separate and additional rich fuel mixture circuit controlled by a plunger on each carb.

As the engine heats up it requires a leaner mixture, therefore the choke/rich is eased off until completely off.

Sounds as if your bike starts well so the mixture is probably rich enough to a bit too rich. When you load the engine it does not perform well until you get out of the range of the rich idle mixture.

IMHO, try a leaner idle adjustment.

Best of success.

Post edited by: bill_wilcox100, at: 2007/12/19 03:25

del

Hey TLH101,

My kz400 is around within a year of your 650 and I had the same problem with mine last year. What kind of carbs due you have? My bike would start ok then run up on RPM's in idle. It also really bogged down when I tried to accelerate.

Turned out to be a torn diaphram that the PO tried to fix with liquid plastic. It definitely caused the bogging, but I'm thinking it affected the idle too 'cause that problem went away when the diaphram was replaced.

Might be worth looking.

Good luck!

I think I might have figured my problem out. What I thought was for syncing the carbs is actually the idle adjustment. I thought the idle mixture screw was the same as the idle adjustment.:whistle: The reason for my confusion is that my idle adjustment isn't a lockable screw; it's just a knob. that leads me to suspect that the vibration of the engine is probably enough to make it move a little and cause unstable idle. I'm going to try and replace it today.

The idle adjust knob should be spring loaded. It does not move under the greatest of vibration. If the spring is missing, replace it and you should be OK.

This should not be the solution to bogging down under load.

This may be a good time to ask if you have a manual. You will want to really consider getting one... don't ask how I know. :whistle:

Best of success.

Z1109R and JMKZHI, thankyou both,I wasn't aware that these machines were jetted lean - I intend re-jetting due to the addition of a 4 into 1 exhaust on my machine.
One size from what I see in the archives.
Thanks again Gentlemen.

An Idle which creeps up after warm up is a lean indication. Either the air screws are opened too far or the idle jets are partially clogged.

I was just at the motorcycle shop and they pulled up the microfiche. And we saw the spring and a washer, which mine is missing. Unfortuanately, the shop guy was messing with the idle adjust screw and now it's out of whack. :S

When I'm looking for the spring, am I going to have to buy an entirely new idle adjust set? The shop guy said they couldn't get the screw. Any suggestions on where to look?

Try Jeff or Rob at Z1 Enterprises Inc.

www.z1enterprises.com/company.aspx

You won't see this part on their site so e-mail or better still give them a call. Be sure you have the Model and Serial number at hand and ask for the spring that adds friction to the Idle speed control knob.

Best of success.

By the way, could you add your Model and Year to your signature to help out would-be contributors... thanks.

del

very good site here for parts....

www.babbittsonline.com/pages/parts/viewbybrand/default.aspx

The spring is there to tension the idle stop screw so it doesn't vibrate loose. Buy a 1/4" spring and washer. Nothing magic about the spring or washer. Most of the idle stop screws are 6mm so 1/4 seems about right. If you have a skinnier idle stop screw, just buy a smaller spring. It has to be long enough where it will provide tension with the screw in the correct position so it can be bought a tad long and snipped off, if necessary.