revs really high when starting cold

77 kz650 c. I usually let it idle for a good five min before taking off. Once its set into gear and moving it tends to want to shoot off into the 6000 rpm range with the throttle entirely closed. I'm pretty sure this is a carb issue. I just don't know where to start looking. Thanks in advance.

I'd start looking for an intake leak. Are there any vacuum ports open that should have a vacuum tube connected to them? Are all the vacuum hoses in good shape no longitudinal splits or cracks of any kind? Lastly, does spraying WD40 on the intake boots affect the idle? If so you've got leaks where the carbs mount up.

Good Luck

KZCSI

check for cracks in the intake boots.

Look at simple things first. You haven't given any hints or history which makes dianosis far more difficult. In other words, did it just start doing this or is this bike new to you and has done this since you have owned it? Oh well, simple... look at the carb holders. The rubber things between engine cylinder head and carburetors that the carb fit into. Do they have VACUUM CAPS on the vacuum ports on the carb holders? If not, there is your problem. Then, look at your throttle cable. If the cables are tight, binding, routed incorrectly or the throttle sleeve is rusty and not lubricated, the same thing will occur. Last, look at the choke plungers; are they all shut when your idle revs up? If so, jiggle the choke plunger lever a bit and see if it comes down. If it does, the rubber pads on the plungers are no longer serviceable... the rubber is shot and they are leaking air. Then check for leaks, as has been suggested by using WD40. A leak will produce white smoke out the exhaust or the bike will die. You can use other stuff but it is pretty flamable and a backfire may make the problem moot.

Sure enough, theres a crack in the intake boot for the carb on the far right side. I'm gonna see if replacing it will remedy the situation.

Thanks for the quick response everyone!

Oh. P.S. I've only had the bike for about a month now, and he problem didn't really start this until a week or so. Who knows what could have happened to it parked on NYC streets...

Post edited by: Boll Weevil, at: 2008/03/04 09:18

Post edited by: Boll Weevil, at: 2008/03/04 19:49

Ok, ran the gamut here. Vacuume covers, fine. The crack in the boot must be superficial as WD-40 test rendered no difference in bike's idle. The choke plunger is fine and the throttle cable (I'm told) was put on three months ago.

As I said, I bought the bike bout a month ago and it was running fine up until last week. It had always been stored indoors up until the last month, where I keep it covered in the street.

Any other options to explore? It seems like their is either too much air or too much fuel hopping in when it ought not to be. If it makes an difference I know I'm running a bit of a rich mixture, as even putting in warm plugs they still get carbon fouled.

Thanks!

Oh! and it usually happens after the bike has been ridden for a few blocks, the problem starts at traffic lights when I take off out of first.

Post edited by: Boll Weevil, at: 2008/03/05 10:36

Has operation of ignition advancer unit (underneath points cover) been checked visually with strobe type timing light to assure it's not sticking in the advanced position?

The advancer should be seen freely moving back and forth as engine is briefly revved by quickly opening and closing throttle.

When the advancer is sticking, it may usually be returned to proper function by just cleaning and lubing.

While at it, would also first clean points, then gap points, then assure ignition timing is set correctly on cylinders 1/4 and also on cylinders 2/3. As known, use the F marks and ignore the T marks.

This may not help with the current problem, but will at least eliminate some suspects.

Good Luck!

Change that carb boot, or all of them. Sounds like once that boot that HAS THE CRACK IN IT gets warm and softer then it lets the air thru, no? The wd40 test might not change your idle, might make it smoke a little, might do nothing at all if you tried it while the boot was still cold and hard. Its GOT to be in that system, or in the cable. Other than that, check the airbox, make sure a mouse didnt make it home and chew thru.. Good luck..

If fitted with a vacuum operated petcock, would assure integrity of vacuum tube running from carb nipple to petcock. If the vacuum tube is cracked or otherwise leaking, it could be allowing intrusion of outside air into the fuel mixture (same as a cracked carb holder or leaking vacuum plug).

If needed -- Z1E Vac-Plug

Good Luck!

Could the interior ignition issues be responsible for the bike sometimes puttering out and losing power, then dying? When this happens it usually starts right back up. Just became a problem riding around the city today running errands. The bike would feel sluggish then die in response to opening throttle.

Should I be taking these kinds of issues to another forum?

Sorry to bombard you guys with questions, but I'm a bit of a novice to most of this, the work I had done some 10yrs ago was on a much much simpler engine, and then dad was always there to help too...

I'm going to get into the ignition system this weekend, advancer unit, points, timing, etc. Though I love the place, living in Brooklyn has its downfalls when it comes to a comfortable work space. Mine happens to be the sidewalk in front of my building where every Tom, Dick and Harry wants to poke their nose in and tell me to open the choke to remedy the problem. Haha.

Thanks again for the help everyone.

-Ben

As this bike is new to you, it would be in your best interest to really go through the maintenance list in your owners manual, and assume nothing has been done.

In my very humble opinion, 6000 rpm is WAY too high for a vacuum leak. I'm sure I've read this wrong.

Examine the throttle system carefully. I'm no expert on your bike, but many KZ's run indepent 'open' and 'close' throttle cables. Perhaps the PO replaced the one but not both? Regardless, you should be able to observe (may have to pull off the tank for clarity) the throttle mechanism on the carburetor bank 'snap' back into position when the throttle is released. Also, you should be able to move the throttle grip 2-3mm before an rpm change is noted at idle. Don't worry too much about the 2-3mm part - do you have some free play in the throttle at idle is the real question. Last but not least, do you notice a change in rpm if you turn the steering stop to stop?

Best of luck, welcome to the forum. Ps. Don't be shy, add your city and state and your bike model to your signature.

Post edited by: Saki Jockey, at: 2008/03/05 21:59

Yeah, I was hoping such a thing was a fairly common problem thus avoiding me having to run the entire maintenance operation from top to bottom. Failing the #2 throttle cable theory I'm gonna do a run over the ignition system then hit the carbs if I have to. Methinks it may not be in the throttle cable as there is no increased RPM when turning side to side at a stop. Although, if there's one thing I've learned, whatever you think the problem may be, its probably not that. Haha.

Post edited by: Boll Weevil, at: 2008/03/06 08:49