TOPIC:

This is on a 1979 KZ650. This has happened both times I've ridden the bike since I got it. Once the engine warms up it will idle around 1500 (my manual hasn't arrived so I'm don't know what it should be) then once I get rolling and ride though a few gears and come to another stop the idle will stay up near 4000. The bike is still new to me so I'm not great at finding the idle adjuster under the tank blindly yet. So I will use the clutch to grab a little bit and it brings it down to around 3000 until I can stop where I have time too look under and adjust the idle. So my question would be would engine vibration be causing the adjuster to unadjust, or is it from an issue with the carbs not closing? The engine runs ok and I don't feel any excessive vibration through the seat or bars. I'm new to carbed bikes so speak to me like I'm stupid if it's a carb issue.

Your idle when warmed up should be 950-1050 rpm.

Do you have a large spring right where you are adjusting the idle? You should have one there. Or it may be there but broken. This spring returns the carbs to an idle position.

Another thing to check would be the throttle cables. Pull off the gas tank and check every inch of the cable, looking for kinks or sharp bends. If you see a kink replace the cable, you can get them for $15.

The cables may be routed wrong and holding the carbs open. Does the idle change when you turn the handlebars from side to side? If it does then the cables are routed wrong. The cables should make large smooth curves from the handlebars thru the forks, into the frame area and onto the carbs.

Also it's a good idea to remove the cables and give them a good cleaning and lube. Before replacing mine I cleaned them with brake cleaner, then shot some oil down the cable. It helped but could not be compared to new cables.

You're going to love this bike

Post edited by: OKC_Kent, at: 2006/03/21 15:40

Four possible causes:

1. bad orings (poorly sealing) on the pilot fuel mixture screws
2. throttle cable has insufficient slack
3. bad rubber pads on choke plungers (they don't seal)
4. Poorly sealing intake manifolds (could be cracked or just real hard or the clamps loose)

Contact me offline if you need further help with this via my web site or by email.

mine did this exact thing and it was air leaking around the carb boots.

I'll check the cables tonight. The carbs have aftermarket stainless filters on each carb but i'll check for bad rubber. I'll have my manual either tomorrow or Friday so I'll be able to give the carbs a good going over and know exactly what parts you guru's are talking about.

OKCKent - I'm adjusting the idle with a little plastic dial under the tank that points up. Should the spring be on the shaft of the dial or by it?

Thanks for everyone's help so far.

It would be next to it. It is a spring about 3 inches long, and it snaps the throttle closed. I was thinking this spring could be broken, but the dual throttle cables would still be able to open and close the carbs. Then I started to think if the cables were kinked or hung up AND this spring was broken, it would give you problems.

But I may be all wet, it's probably air leaks.

Puckaveli, carbs and idle problems can be fickled to work with and until you know that there are no air leaks, and the all the o-rings are good, and that the carbs are clean inside and working smooth, you will be working in the dark. Even after I rebuilt my carbs and replaced the rubber o-rings and had no air leaks, my idle would change as the bike got up to normal temps. I was forever adjusting the throttle stop knob to slow the idle down as I rode and came to stops, then I'd be turning the idle back up when the bike was colder again. Once WiredGeorge sync'd my carbs and we got the air mixture/idle adjusted, the bike has stayed exactly where it is supposed to be, idling around 950 rpms all the time after the choke is off.

If you are unsure about messing with the carbs, contact WiredGeorge through his website or directly. He is the "carb man" and knows his stuff!

Good luck!

Ok, I figured out why the idle stays high. I was lubbing the cable and looked in my manual and the picture shows 2 cables. The bike didn't have the close cable on it when I bought it so I didn't know it was supposed to have 2. Man, I feel stupid and relieved at the same time.

puckaveli wrote:

Ok, I figured out why the idle stays high. I was lubbing the cable and looked in my manual and the picture shows 2 cables. The bike didn't have the close cable on it when I bought it so I didn't know it was supposed to have 2. Man, I feel stupid and relieved at the same time.

Man I hate to burst your bubble, but that's not it. THe second cable is not necessary to function correctly, it is just kinda a backup in case the spring and other cable broke.

I have read one cable is open and the other is close. The close cable is missing. It might not be the only reason it's wandering but it is a factor. Even between shifts the rpm's stay up, which to me means the throttle plate isn't closing. Once I get it on I'll have a better idea of what's going on.

puckaveli wrote:

I have read one cable is open and the other is close. The close cable is missing. It might not be the only reason it's wandering but it is a factor. Even between shifts the rpm's stay up, which to me means the throttle plate isn't closing. Once I get it on I'll have a better idea of what's going on.

i yanked the second cable off my 79 kz900 2 years ago...runs fine. the missing second cable is really not an issue.

is that anything like wandering aimlessly?i seem to do a lot of that nowadays that im not working any more!